is_shared() fixes

We can assume that the path is not shared only when the path exist (file or directory) and get_shares() thrown 404 exception.
Good idea, but I didn't know how to do it... now I know (thanks to your other project: https://github.com/PVince81/ocshareplasmoid) :smile:
Fixed @ 78d0cfb91e787685e1d5088bafee12d116794266