This patch is an attempt to cope with Genesys Logic's, shall we say,
creative approach to implementing the USB protocols.  Their high-speed
mass storage devices sometimes add an excess 0-length packet to the end of
a data phase transmission.  Of course we don't read that packet as part of
the data phase; we see it as a 0-length CSW message.  The real CSW follows
immediately after.  (Or sometimes a STALL follows immediately after, with
the real CSW coming after that!)

The patch checks the results of the first attempt to read the CSW.  If it
sees a normal packet (not a STALL) with length 0, it retries the read.
Reports from two users indicate that it improves the performance of their
USB-2 DVD drives.