Handling for EOF reading error in gzipped content

Hi!
Today I had a crash in mitmproxy when I tried viewing some failed response. It was an unhandled EOFException in libmproxy/encoding.py, decode_gzip function.
Adding it to the except block seems the right thing to do.
Unfortunately, mitmproxy hanged the terminal as well, and I could not collect the session for further use/testing.