Fix warning -Wgnu-zero-variadic-macro-arguments (#1384)

3rdparty/dear-imgui/imconfig.h

@@ -15,7 +15,7 @@
 
 //---- Define assertion handler. Defaults to calling assert().
 #include <assert.h>
-#define IM_ASSERT(_EXPR, ...) assert(_EXPR)
+#define IM_ASSERT(_EXPR) assert(_EXPR)
 
 //---- Define attributes of all API symbols declarations, e.g. for DLL under Windows.
 //#define IMGUI_API __declspec( dllexport )