Fix NPE in RoomInfo when subject has not value

All three form fields accessed had the same issue and are now fixed.

Can you take a look into it and review, if we need that for 2.6.0 RC2 or 2.6.0 final?

According to a community report this has to reopen

http://community.igniterealtime.org/message/208940#208940

This issue is not fixed, the patch does not work correctly.

This is still an issue in v3.1.0. RoomInfo ctor throws an NPE when connecting to an ejabberd server.

The code was changed from

this.subject = form.getField("muc#roominfo_subject").getValues().next();

to

Iterator<String> values = form.getField("muc#roominfo_subject").getValues();
if (values.hasNext()) {
this.subject = values.next();
}
else {
this.subject = "";
}

The correct fix is:

final FormField subjField = form.getField("muc#roominfo_subject");
this.subject = subjField == null ? "" : subjField.getValues().next();

Note that description has potentially the same problem.