Don't try to build form for "None" backend.
Don't try to build form for "None" backend.

Fix #6266

annando/friendica,friendica/friendica,friendica/friendica,fabrixxm/friendica,annando/friendica,tobiasd/friendica,tobiasd/friendica,tobiasd/friendica,annando/friendica,friendica/friendica,annando/friendica,fabrixxm/friendica,fabrixxm/friendica,fabrixxm/friendica,fabrixxm/friendica,tobiasd/friendica,tobiasd/friendica,friendica/friendica,annando/friendica,friendica/friendica