Instead of keying on the packet being received, key on buffer empty.

This should work exactly the same, but is more correct.  It's possible
that in the future, packet data could be added to the buffer after
receiveBufPos, and we could know that no more is required.

3rdp/build/cl-make-channels-work.patch

@@ -23,7 +23,7 @@
 +		if (*bytesCopied > 0) {
 +			if (sessionInfoPtr->type == CRYPT_SESSION_SSH || sessionInfoPtr->type == CRYPT_SESSION_SSH_SERVER)
 +				{
-+				if (sessionInfoPtr->pendingPacketLength <= 0)
++				if (sessionInfoPtr->receiveBufPos <= 0)
 +					{
 +					status = OK_SPECIAL;
 +					}