GLSL: Fix Khronos private Bugzilla 15973: local sizes can't be 0.

Test/310.comp

@@ -4,7 +4,7 @@ layout(local_size_x = 2) in;
 layout(local_size_x = 16) in;     // ERROR, changing
 layout(local_size_z = 4096) in;   // ERROR, too large
 layout(local_size_x = 2) in;
-
+layout(local_size_y = 0) in;      // ERROR, 0 not allowed
 const int total = gl_MaxComputeWorkGroupCount.y 
                 + gl_MaxComputeUniformComponents
                 + gl_MaxComputeTextureImageUnits

Test/450.comp

 #version 450 core
+layout(local_size_x = 0) in; // ERROR, 0 not allowed
\ No newline at end of file

Test/baseResults/310.comp.out

 310.comp
 ERROR: 0:4: 'local_size' : cannot change previously set size 
 ERROR: 0:5: 'local_size' : too large; see gl_MaxComputeWorkGroupSize 
+ERROR: 0:7: 'local_size_y' : must be at least 1 
 ERROR: 0:23: '' : array size required 
 ERROR: 0:39: 'in' : global storage input qualifier cannot be used in a compute shader 
 ERROR: 0:39: 'location qualifier on input' : not supported in this stage: compute
@@ -83,7 +84,7 @@ WARNING: 0:238: '#define' : names containing consecutive underscores are reserve
 ERROR: 0:244: 'gl_DeviceIndex' : required extension not requested: GL_EXT_device_group
 ERROR: 0:245: 'gl_ViewIndex' : undeclared identifier 
 ERROR: 0:255: 'gl_ViewIndex' : undeclared identifier 
-ERROR: 82 compilation errors.  No code generated.
+ERROR: 83 compilation errors.  No code generated.
 
 
 Shader version: 310

Test/baseResults/450.comp.out

 450.comp
+ERROR: 0:2: 'local_size_x' : must be at least 1 
+ERROR: 1 compilation errors.  No code generated.
+
+
 Shader version: 450
 local_size = (1, 1, 1)
-0:? Sequence
+ERROR: node is still EOpNull!
 0:?   Linker Objects
 
 
@@ -11,6 +15,6 @@ ERROR: Linking compute stage: Missing entry point: Each stage requires one entry
 
 Shader version: 450
 local_size = (1, 1, 1)
-0:? Sequence
+ERROR: node is still EOpNull!
 0:?   Linker Objects
 

glslang/MachineIndependent/ParseHelper.cpp

@@ -4260,6 +4260,10 @@ void TParseContext::setLayoutQualifier(const TSourceLoc& loc, TPublicType& publi
         if (id.compare(0, 11, "local_size_") == 0) {
             profileRequires(loc, EEsProfile, 310, 0, "gl_WorkGroupSize");
             profileRequires(loc, ~EEsProfile, 430, E_GL_ARB_compute_shader, "gl_WorkGroupSize");
+            if (id.size() == 12 && value == 0) {
+                error(loc, "must be at least 1", id.c_str(), "");
+                return;
+            }
             if (id == "local_size_x") {
                 publicType.shaderQualifiers.localSize[0] = value;
                 return;