[#6922] ticket:501 Fixed freeze when importing issue tracker

  Chenged regexp to match image URL
[#6922] ticket:501 Fix a couple of AttributeErrors on None
[#6922] Regexp cleanup to prevent freeze on any other unmatched chars

The ([...]+)* construct was causing the regexp parser to hang when the
[...] block didn't match.  [42e29a] fixed the proximate cause of the
freezes (filenames including % chars), but that construct was weird
and pointless anyway.

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>