Fix bug introduced by checkin 22920, allow large

Fix bug introduced by checkin 22920, allow large
readX. Fix from Dmitry Shatrov <dhsatrov@linux.vnet.ibm.com>.

"In send_file_readX(), if startpos > sbuf.st_size, then smb_maxcnt is set
to an invalid large value due to integer overflow.
As for me, this resulted in MS Word hanging while trying to save
a 1.5Mb document."

This isn't in shipping code.

Jeremy.

git-svn-id: svn+ssh://svn.samba.org/data/svn/samba/branches/SAMBA_3_0@23752 0c0555d6-39d7-0310-84fc-f1cc0bd64818