autofs: fix invalid header 'number of entries' in packet
Pointer to packet body may change while filling packet with autofs
mount points. As a consequence, we sometimes wrote the number of
entries into invalid body and we recieved an arbitrary number
on the client side.
If the number was 0, there were some skipped entries. If the number
was greater than 0, everything worked correctly, because we iterate
through the cached entries until we reach packet length - we don't
compare to the number.