added missing return statement after showForm call

added missing return statement after showForm call

Issue #3125 at http://status.net/open-source/issues/3125 (and its duplicate 3127) describe buggy behaviour when trying to create a new group - i.e. the group is still created but with nickname NULL.

The reason the group is created is that when failing Nickname::normalize, the function trySave() in actions/newgroup.php doesn't call 'return' - meaning it just keeps going despite the error thrown. It a

So the simple solution to this bug was adding a return call at line 128, inside the catch just after the showForm(...) call.