Wrap object handler in try...except

[robert-nix]

Currently if you do something like unityextract --images *.unity3d in Hearthstone/Data/Win it'll break on a few objects due to library/unity default resources being missing; it's nice to be able to continue extraction when that happens.

[jleclanche]

There's too much stuff going on here. If you update this to just be a try ... except Exception: with a sys.stderr.write instead of print() I can merge it, otherwise leaving it out.