Fix bug with NSConcreteMutableAttributedString in iOS6

2014-02-05 02:38:09.350 Presentice[11657:907] *** Assertion failure in
-[NSConcreteMutableAttributedString
boundingRectWithSize:options:context:],
/SourceCache/UIFoundation/UIFoundation-78/UIFoundation/TextSystem/NSStri
ngDrawing.m:1176
2014-02-05 02:38:09.352 Presentice[11657:907] *** Terminating app due
to uncaught exception 'NSInternalInconsistencyException', reason:
'NSAttributedString invalid for autoresizing, it must have a single
spanning paragraph style (or none) with a non-wrapping lineBreakMode.'