Fixed narrowing conversion warning.

src/glcontext_wgl.cpp

@@ -217,7 +217,7 @@ namespace bgfx
 				// create context will fail and it will error out there.
 				BX_WARN(result, "SetPixelFormat failed (last err: 0x%08x)!", GetLastError() );
 
-				uint32_t flags = BGFX_CONFIG_DEBUG ? WGL_CONTEXT_DEBUG_BIT_ARB : 0;
+				int32_t flags = BGFX_CONFIG_DEBUG ? WGL_CONTEXT_DEBUG_BIT_ARB : 0;
 				BX_UNUSED(flags);
 				int32_t contextAttrs[9] =
 				{