Don't overwrite settings when no pep8 config file exists.
Don't overwrite settings when no pep8 config file exists.

The pep8 module always returns a config file, even when one doesn't
exists. When it doesn't, it means pep8 merely read the defaults, so
don't overwrite ST's settings.

Fixes issue #4.

SublimeLinter/SublimeLinter-pep8