Fix crash when stopping and starting a game with OpenCL enabled

git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@5047 8ced0084-cf51-0410-be5f-012b33b47a6e

Source/Core/Common/Src/OpenCL.cpp

@@ -180,6 +180,10 @@ void Destroy()
 		return;
 	clReleaseCommandQueue(g_cmdq); 
 	clReleaseContext(g_context);
+	g_context = NULL;
+	g_cmdq = NULL;
+	
+	g_bInitialized = false;
 #endif
 }