An empty string is an empty callerid ... so zap it. This closes issue #10502, which was pointed out by dswartz. Thank you, and may the swartz be with you

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@80878 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_zapateller.c

@@ -85,7 +85,7 @@ static int zapateller_exec(struct ast_channel *chan, void *data)
 			res = ast_safe_sleep(chan, 500);
 		}
 	}
-	if (chan->cid.cid_num && nocallerid) {
+	if (!ast_strlen_zero(chan->cid.cid_num) && nocallerid) {
 		ast_module_user_remove(u);
 		return res;
 	}