Fix hex output in share names

Enumshares occasionally returns share names as hex instead of
ascii/text output. This commit checks the individual strings
returned by the module for \x00\x00 and converts those matching
the pattern to text (Rex::Text.to_ascii(str)).

Testing:
  Run against win7 x64 workstations and review output, apply patch
  repeat.

Possible TODO: find a better way to ID hex strings as \x00\x00 may
not always be present, although it has been so far in tests