ogl: fix single core crash

osx is missing, sorry but I'm too stupid for objective-c

Source/Core/DolphinWX/Src/GLInterface/WGL.h

@@ -33,6 +33,7 @@ public:
 	void UpdateFPSDisplay(const char *Text);
 	bool Create(void *&window_handle);
 	bool MakeCurrent();
+	bool ClearCurrent();
 	void Shutdown(); 
 
 	void Update();