badfiles: Fix decoding for command output

Probably fixes #3165. There were several things going wrong here:

1. For some reason, this was using the *filesystem* encoding, which is
   what you use to decode filenames. But this was general command
   output, not filenames.
2. Errors in decoding threw exceptions, even though all we do with this
   output is show it to the user.
3. The prints were using `displayable_path`, even though the lines are
   *already* Unicode strings.

Hopefully this cleans up that mess.

beetsplug/badfiles.py

@@ -66,7 +66,7 @@ def run_command(self, cmd):
             status = e.returncode
         except OSError as e:
             raise CheckerCommandException(cmd, e)
-        output = output.decode(sys.getfilesystemencoding())
+        output = output.decode(sys.getdefaultencoding(), 'replace')
         return status, errors, [line for line in output.split("\n") if line]
 
     def check_mp3val(self, path):
@@ -134,12 +134,12 @@ def check_item(self, item):
             ui.print_(u"{}: checker exited with status {}"
                       .format(ui.colorize('text_error', dpath), status))
             for line in output:
-                ui.print_(u"  {}".format(displayable_path(line)))
+                ui.print_(u"  {}".format(line))
         elif errors > 0:
             ui.print_(u"{}: checker found {} errors or warnings"
                       .format(ui.colorize('text_warning', dpath), errors))
             for line in output:
-                ui.print_(u"  {}".format(displayable_path(line)))
+                ui.print_(u"  {}".format(line))
         elif self.verbose:
             ui.print_(u"{}: ok".format(ui.colorize('text_success', dpath)))
 

docs/changelog.rst

@@ -147,6 +147,9 @@ Fixes:
   Thanks to :user:`Holzhaus`.
   :bug:`1579`
 * Fetchart now respects the ``ignore`` and ``ignore_hidden`` settings. :bug:`1632`
+* :doc:`/plugins/badfiles`: Avoid a crash when the underlying tool emits
+  undecodable output.
+  :bug:`3165`
 
 .. _python-itunes: https://github.com/ocelma/python-itunes