give useful data when not finding a given shader var

Engine/source/gfx/gl/gfxGLShader.cpp

@@ -661,7 +661,7 @@ void GFXGLShader::initHandles()
       // Index element 1 of the name to skip the '$' we inserted earier.
       GLint loc = glGetUniformLocation(mProgram, &desc.name.c_str()[1]);
 
-      AssertFatal(loc != -1, "");
+      AssertFatal(loc != -1, avar("uniform %s in shader file Vert: (%s) Frag: (%s)", &desc.name.c_str()[1], mVertexFile.getFullPath().c_str(), mPixelFile.getFullPath().c_str()));
 
       HandleMap::Iterator handle = mHandles.find(desc.name);
       S32 sampler = -1;