Improove Exception handling

[ricco386]

Install the library and try to execute dodgy script in the directory where are no Python files. Instead of the stack trace, I would imagine an error message or at least empty dict...

<mock-chroot> sh-4.4# dodgy
Traceback (most recent call last):
  File "/usr/bin/dodgy", line 4, in <module>
    dodgy.run.run()
  File "/usr/lib/python2.7/site-packages/dodgy/run.py", line 56, in run
    warnings = run_checks(os.getcwd())
  File "/usr/lib/python2.7/site-packages/dodgy/run.py", line 44, in run_checks
    for msg_parts in check_file(filepath):
  File "/usr/lib/python2.7/site-packages/dodgy/checks.py", line 72, in check_file
    return check_file_contents(to_check.read())
  File "/usr/lib64/python2.7/codecs.py", line 686, in read
    return self.reader.read(size)
  File "/usr/lib64/python2.7/codecs.py", line 492, in read
    newchars, decodedbytes = self.decode(data, self.errors)
UnicodeDecodeError: 'utf8' codec can't decode byte 0x8b in position 1: invalid start byte

<mock-chroot> sh-4.4# dodgy-3.6 
Traceback (most recent call last):
  File "/usr/bin/dodgy-3.6", line 4, in <module>
    dodgy.run.run()
  File "/usr/lib/python3.6/site-packages/dodgy/run.py", line 56, in run
    warnings = run_checks(os.getcwd())
  File "/usr/lib/python3.6/site-packages/dodgy/run.py", line 44, in run_checks
    for msg_parts in check_file(filepath):
  File "/usr/lib/python3.6/site-packages/dodgy/checks.py", line 72, in check_file
    return check_file_contents(to_check.read())
  File "/usr/lib64/python3.6/codecs.py", line 698, in read
    return self.reader.read(size)
  File "/usr/lib64/python3.6/codecs.py", line 501, in read
    newchars, decodedbytes = self.decode(data, self.errors)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8b in position 1: invalid start byte