Fix searching from OS X cmdline

Fix searching from OS X cmdline

Searching from OS X cmdline with `mdfind` will generate queries with
an empty query attribute array. In that case we must add a nil element
for every query match to the filemeta array.

Also fixed:
* marshalling of empty CNID arrays and filemeta
* return 0x23 instead of 0 when returning a non empty result list, this
  is was traces of an OS X AFP server show