Fix the non_interactive() function used in WML tests

The function previously returned false, even in non-interactive
scenarios like in WML tests. This fixes the function to return the
expected values.

src/video.cpp

@@ -241,7 +241,7 @@ bool non_interactive()
 	if (fake_interactive)
 		return false;
 #if SDL_VERSION_ATLEAST(2, 0, 0)
-	return false;
+	return window == NULL;
 #else
 	return SDL_GetVideoSurface() == NULL;
 #endif