Fixes according to e-mail.

Since the default quality is implicit in PIL, there is no need to pass this argument if it was not explicitly specified. Also quality does not need to be an int, it can be a string too, see:
https://github.com/python-imaging/Pillow/blob/master/PIL/JpegPresets.py

This is why I chose not to pass it at all, if it is not specified.