Windows: Fix editor icons and other potential breakage related to HINSTACE

I even wrote the function for this but forgot to use it. Probably due to
hope that someone would replace that stuff with GetModuleHandle(0).

src/C4WinMain.cpp

@@ -110,6 +110,7 @@ int WINAPI WinMain (HINSTANCE hInst,
 		LocalFree(wargv);
 
 		// Init application
+		Application.SetInstance(hInst);
 		if (!Application.Init(argv.size(), &argv[0]))
 		{
 			Application.Clear();