MAVFTP can't show folders with ":" in them

@tridge has found that MP can't handle these situations:

- can't handle filenames or folders (?) with a colon in the name

Start by locating the MAVFTP implementation and the folder or filename listing entry point in Mission Planner, then reproduce a listing containing a colon in a folder or filename. Trace where that name is parsed or displayed and verify that the affected item appears correctly without breaking other listings.

Written by the indexing model from the issue text.