vfs_fruit: filter empty streams

vfs_fruit: filter empty streams

First step in achieving macOS compliant behaviour wrt to empty streams:
- hide empty streams in streaminfo
- prevent opens of empty streams

This means that we may carry 0-byte sized streams in our streams
backend, but this shouldn't really hurt.

The previous attempt of deleting the streams when an SMB setinfo eof to
0 request came in, turned out be a road into desaster.

We could set delete-on-close on the stream, but that means we'd have to
check for it for every write on a stream and checking the
delete-on-close bits requires fetching the locking.tdb record, so this
is expensive and I'd like to avoid that overhead.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13646

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>