COM0 and LPT0 are not listed in the official Microsoft's documentation
at https://docs.microsoft.com/windows/win32/fileio/naming-a-file, but
in reality are also invalid in Windows Explorer.
Signed-off-by: Tomasz Wilczyński <twilczynski@naver.com>
Add specific errors for the failures, resulting in this rather than just
the generic "invalid filename":
[MRIW7] 08:50:50 INFO: Puller (folder default, item "NUL"): syncing: filename is invalid: name is reserved
[MRIW7] 08:50:50 INFO: Puller (folder default, item "fail."): syncing: filename is invalid: name ends with space or period
[MRIW7] 08:50:50 INFO: Puller (folder default, item "sup:yo"): syncing: filename is invalid: name contains reserved character
[MRIW7] 08:50:50 INFO: default: Failed to sync 3 items
