$wgEnotifUseRealName: Check, if realname is non-empty

When $wgEnotifUseRealName is true and no realname is given, the email
notification will contain a empty string, so checking the realname first

Change-Id: I1b76d9eae8ada8ca2eee8fa93d7119fbff44269d
Merge "$wgEnotifUseRealName: Check, if realname is non-empty"