Catch LabelTTF errors

[seagullua]

In some cases, LabelTTF can fire exceptions, which stops whole cocos from working. We have collected a bunch of errors from Sentry and added try/catch in places where the errors have occurred in real players.

[pandamicro]

try catch will have significant impact on performance, can you be more specific about the issues you met ? I think we can add some defensive code, but try catch may not be a good idea