Catch exception when reading EXIF

@heynemann You are right, specifying the actual exceptions are better practice. However this case is not that neat. I read about the pexif [source code](https://github.com/thumbor/pexif/blob/master/pexif.py) and there are several exceptions, what's worse, they are directly derived from Exception and nested in other classes. The code here would be:
```
except DefaultSegment.InvalidSegment, JpegFile.SkipTag, JpegFile.InvalidFile, JpegFile.NoSection
```
But my intention here is no matter what error occurs during reading EXIF, the engine just ignore it. It shouldn't worried about so much details down there.

I think the best solution here is that pexif has a base exception class called ExIfException, then we are all happy.  Unfortunately there isn't. If you do think listing all the exceptions like above is better, I'm ok with that and I will do it.