Remapper: make remapper robust against non-exiting error handlers

Remapper errors are generally fatal: there has been some unexpected situation while
parsing the SPV binary, and there is no reasonable way to carry on.  The
errorHandler() function is called in this case, which by default exits, but
it is possible to submit a handler which does not.  In that case the remapper would
carry on in a bad state.

This change ensures a graceful termination of the remap() function.

While a try {} catch {} construct would be the ideal and safe way to do this,
that's off limits for certain environments, so this tries to do the same thing
with explicit code, to catch all the bailout paths.
diff --git a/Test/runtests b/Test/runtests
index 3cceb43..5e873f5 100755
--- a/Test/runtests
+++ b/Test/runtests
@@ -3,6 +3,7 @@
 TARGETDIR=localResults
 BASEDIR=baseResults
 EXE=../build/install/bin/glslangValidator
+REMAPEXE=../build/install/bin/spirv-remap
 HASERROR=0
 mkdir -p localResults
 
@@ -141,6 +142,7 @@
 #
 # Testing -D and -U
 #
+echo "Testing -D and -U"
 $EXE -DUNDEFED -UIN_SHADER -DFOO=200 -i -l -UUNDEFED -DMUL=FOO*2 glsl.-D-U.frag > $TARGETDIR/glsl.-D-U.frag.out
 diff -b $BASEDIR/glsl.-D-U.frag.out $TARGETDIR/glsl.-D-U.frag.out || HASERROR=1
 $EXE -D -e main -V -i -DUNDEFED -UIN_SHADER -DFOO=200 -UUNDEFED hlsl.-D-U.frag > $TARGETDIR/hlsl.-D-U.frag.out
@@ -149,6 +151,7 @@
 #
 # Test --client and --target-env
 #
+echo "Testing --client and --target-env"
 $EXE --client vulkan100      spv.targetVulkan.vert || HASERROR=1
 $EXE --client opengl100      spv.targetOpenGL.vert || HASERROR=1
 $EXE --target-env vulkan1.0  spv.targetVulkan.vert || HASERROR=1
@@ -159,6 +162,7 @@
 #
 # Testing GLSL entry point rename
 #
+echo "Testing GLSL entry point rename"
 $EXE -H -e foo --source-entrypoint main glsl.entryPointRename.vert > $TARGETDIR/glsl.entryPointRename.vert.out
 diff -b $BASEDIR/glsl.entryPointRename.vert.out $TARGETDIR/glsl.entryPointRename.vert.out || HASERROR=1
 $EXE -H -e foo --source-entrypoint bar glsl.entryPointRename.vert > $TARGETDIR/glsl.entryPointRename.vert.bad.out
@@ -167,6 +171,15 @@
 diff -b $BASEDIR/glsl.entryPointRename2.vert.out $TARGETDIR/glsl.entryPointRename2.vert.out || HASERROR=1
 
 #
+# Testing remapper error handling
+#
+echo "Testing remapper error handling"
+$REMAPEXE --do-everything -i remap.invalid-spirv-1.spv -o $TARGETDIR > $TARGETDIR/remap.invalid-spirv-1.out && HASERROR=1
+diff -b $BASEDIR/remap.invalid-spirv-1.out $TARGETDIR/remap.invalid-spirv-1.out || HASERROR=1
+$REMAPEXE --do-everything -i remap.invalid-spirv-2.spv -o $TARGETDIR > $TARGETDIR/remap.invalid-spirv-2.out && HASERROR=1
+diff -b $BASEDIR/remap.invalid-spirv-2.out $TARGETDIR/remap.invalid-spirv-2.out || HASERROR=1
+
+#
 # Final checking
 #
 if [ $HASERROR -eq 0 ]