Corrects error handling in AttachShader
TRAC #11659
Signed-off-by: Nicolas Capens
Signed-off-by: Daniel Koch

Author:    Shannon Woods

git-svn-id: https://angleproject.googlecode.com/svn/trunk@129 736b8ea6-26fd-11df-bfd4-992fa37f6226
diff --git a/src/libGLESv2/libGLESv2.cpp b/src/libGLESv2/libGLESv2.cpp
index 8260525..7f1dc31 100644
--- a/src/libGLESv2/libGLESv2.cpp
+++ b/src/libGLESv2/libGLESv2.cpp
@@ -65,9 +65,28 @@
             gl::Program *programObject = context->getProgram(program);
             gl::Shader *shaderObject = context->getShader(shader);
 
-            if (!programObject || !shaderObject)
+            if (!programObject)
             {
-                return error(GL_INVALID_VALUE);
+                if (context->getShader(program))
+                {
+                    return error(GL_INVALID_OPERATION);
+                }
+                else
+                {
+                    return error(GL_INVALID_VALUE);
+                }
+            }
+
+            if (!shaderObject)
+            {
+                if (context->getProgram(shader))
+                {
+                    return error(GL_INVALID_OPERATION);
+                }
+                else
+                {
+                    return error(GL_INVALID_VALUE);
+                }
             }
 
             if (!programObject->attachShader(shaderObject))