res_parking: Fix bug where reloading immediately wipes new parkpos extensions

(closes issue ASTERISK-22631)
Reported by: Kevin Harwell
........

Merged revisions 401158 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@401159 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_parking.c

@@ -623,6 +623,9 @@ void parking_lot_cfg_remove_extensions(struct parking_lot_cfg *lot_cfg)
 		 */
 		ast_context_destroy(NULL, lot_cfg->registrar);
 	}
+
+	/* If we come back for a second pass, someone else has this registrar now. */
+	ast_string_field_set(lot_cfg, registrar, "");
 }
 
 static void remove_all_configured_parking_lot_extensions(void)