Semantics: 'invocations' defaults to 1, not 0.

'invocations' was using 0 as the "shader never set" flag and as the
default. Formalize this and explicit set to 1 and link time.
diff --git a/Test/baseResults/410.geom.out b/Test/baseResults/410.geom.out
index b1f5a57..6f7252c 100644
--- a/Test/baseResults/410.geom.out
+++ b/Test/baseResults/410.geom.out
@@ -12,7 +12,7 @@
 
 
 Shader version: 410
-invocations = 0
+invocations = -1
 max_vertices = -1
 input primitive = none
 output primitive = none
@@ -65,7 +65,7 @@
 ERROR: Linking geometry stage: At least one shader must specify a layout(max_vertices = value)
 
 Shader version: 410
-invocations = 0
+invocations = 1
 max_vertices = -1
 input primitive = none
 output primitive = none
diff --git a/Test/baseResults/420.geom.out b/Test/baseResults/420.geom.out
index fdb2cc8..416df13 100644
--- a/Test/baseResults/420.geom.out
+++ b/Test/baseResults/420.geom.out
@@ -10,7 +10,7 @@
 
 
 Shader version: 420
-invocations = 0
+invocations = -1
 max_vertices = -1
 input primitive = triangles
 output primitive = none
@@ -137,7 +137,7 @@
 ERROR: Linking geometry stage: At least one shader must specify a layout(max_vertices = value)
 
 Shader version: 420
-invocations = 0
+invocations = 1
 max_vertices = -1
 input primitive = triangles
 output primitive = none
diff --git a/Test/baseResults/420_size_gl_in.geom.out b/Test/baseResults/420_size_gl_in.geom.out
index 577c246..21d1944 100644
--- a/Test/baseResults/420_size_gl_in.geom.out
+++ b/Test/baseResults/420_size_gl_in.geom.out
@@ -5,7 +5,7 @@
 
 
 Shader version: 420
-invocations = 0
+invocations = -1
 max_vertices = -1
 input primitive = triangles
 output primitive = none
@@ -44,7 +44,7 @@
 ERROR: Linking geometry stage: At least one shader must specify a layout(max_vertices = value)
 
 Shader version: 420
-invocations = 0
+invocations = 1
 max_vertices = -1
 input primitive = triangles
 output primitive = none
diff --git a/Test/baseResults/450.geom.out b/Test/baseResults/450.geom.out
index 0876a0c..fd98d08 100644
--- a/Test/baseResults/450.geom.out
+++ b/Test/baseResults/450.geom.out
@@ -2,7 +2,7 @@
 Warning, version 450 is not yet complete; most version-specific features are present, but some are missing.
 
 Shader version: 450
-invocations = 0
+invocations = -1
 max_vertices = -1
 input primitive = none
 output primitive = none
@@ -40,7 +40,7 @@
 ERROR: Linking geometry stage: At least one shader must specify a layout(max_vertices = value)
 
 Shader version: 450
-invocations = 0
+invocations = 1
 max_vertices = -1
 input primitive = none
 output primitive = none
diff --git a/Test/baseResults/mains1.frag.out b/Test/baseResults/mains1.frag.out
index 140dae8..8ba02bf 100644
--- a/Test/baseResults/mains1.frag.out
+++ b/Test/baseResults/mains1.frag.out
@@ -18,7 +18,7 @@
 
 
 Shader version: 150
-invocations = 0
+invocations = -1
 max_vertices = -1
 input primitive = none
 output primitive = points
@@ -29,7 +29,7 @@
 
 noMain2.geom
 Shader version: 150
-invocations = 0
+invocations = -1
 max_vertices = -1
 input primitive = none
 output primitive = line_strip
@@ -52,7 +52,7 @@
     main(
 
 Shader version: 150
-invocations = 0
+invocations = 1
 max_vertices = -1
 input primitive = none
 output primitive = points
diff --git a/Test/baseResults/max_vertices_0.geom.out b/Test/baseResults/max_vertices_0.geom.out
index 85f2e38..94890bc 100644
--- a/Test/baseResults/max_vertices_0.geom.out
+++ b/Test/baseResults/max_vertices_0.geom.out
@@ -1,6 +1,6 @@
 max_vertices_0.geom
 Shader version: 330
-invocations = 0
+invocations = -1
 max_vertices = 0
 input primitive = points
 output primitive = triangle_strip
@@ -19,7 +19,7 @@
 
 
 Shader version: 330
-invocations = 0
+invocations = 1
 max_vertices = 0
 input primitive = points
 output primitive = triangle_strip
diff --git a/Test/baseResults/spv.150.geom.out b/Test/baseResults/spv.150.geom.out
index e3efab7..46901dc 100755
--- a/Test/baseResults/spv.150.geom.out
+++ b/Test/baseResults/spv.150.geom.out
@@ -12,7 +12,7 @@
                               MemoryModel Logical GLSL450
                               EntryPoint Geometry 4  "main" 18 70 10 29 33
                               ExecutionMode 4 InputTrianglesAdjacency
-                              ExecutionMode 4 Invocations 0
+                              ExecutionMode 4 Invocations 1
                               ExecutionMode 4 OutputTriangleStrip
                               ExecutionMode 4 OutputVertices 30
                               Source GLSL 150
diff --git a/Test/baseResults/spv.330.geom.out b/Test/baseResults/spv.330.geom.out
index 1f310bb..2d48b2f 100755
--- a/Test/baseResults/spv.330.geom.out
+++ b/Test/baseResults/spv.330.geom.out
@@ -12,7 +12,7 @@
                               MemoryModel Logical GLSL450
                               EntryPoint Geometry 4  "main" 20 13
                               ExecutionMode 4 Triangles
-                              ExecutionMode 4 Invocations 0
+                              ExecutionMode 4 Invocations 1
                               ExecutionMode 4 OutputTriangleStrip
                               ExecutionMode 4 OutputVertices 3
                               Source GLSL 330