Clear up a C++ compile warning

glslang/Include/ConstantUnion.h

@@ -43,6 +43,8 @@ class TConstUnion {
 public:
     POOL_ALLOCATOR_NEW_DELETE(GetThreadPoolAllocator())
 
+    TConstUnion() : iConst(0), type(EbtInt) { }
+
     void setIConst(int i)
     { 
         iConst = i;