res/res_musiconhold: Add a warning when MOH does not exist

Change-Id: Ifdfbd0b97cf31478d29923ec30aabce28d01740b

res/res_musiconhold.c

@@ -881,7 +881,7 @@ static struct mohclass *_get_mohbyname(const char *name, int warn, int flags, co
 #endif
 
 	if (!moh && warn) {
-		ast_debug(1, "Music on Hold class '%s' not found in memory\n", name);
+		ast_log(LOG_WARNING, "Music on Hold class '%s' not found in memory. Verify your configuration.\n", name);
 	}
 
 	return moh;