app: check if both restored and initialized flags are set to determine…

… whether the program is really ready to accept various commands.

In particular, on macOS, one could drop an image to the app icon in the
dock while starting up (visible splash). Then if the profile convert
dialog appears *behind* the splash, it would block loading until an
action is taken (unfortunately as it's hidden, people may miss it and
would think GIMP froze), as reported by cyril and reproduced by lukaso.

I can't test myself, but I'm hoping this will fix the issue (similar to
commit a86ed68870 where we had a similar issue with dbus file opening
on Linux).

app/core/gimp.c

@@ -876,7 +876,7 @@ gimp_is_restored (Gimp *gimp)
 {
   g_return_val_if_fail (GIMP_IS_GIMP (gimp), FALSE);
 
-  return gimp->restored;
+  return gimp->initialized && gimp->restored;
 }
 
 /**