SMB: fix parsing of "net usershare info".
At least Samba version >=4.14.12 and <=4.16.2 generate a trailing comma with "net usershare info" like so:
claus@anaxagoras /usr/local/storage/a/samba/public $ net usershare info [scanbox] usershare_acl=ANAXAGORAS\claus:R,Everyone:R,ANAXAGORAS\scanner-upload:F,
OTOH, "net usershare add" does not accept a trailing comma as input and generates an error message:
net usershare add: malformed acl (missing ':').