Don't send an empty SSPI negotiation packet at the end of the negotiation.

Fixes bug #3750

src/interfaces/libpq/fe-auth.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-auth.c,v 1.133 2007/11/15 21:14:46 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/interfaces/libpq/fe-auth.c,v 1.134 2007/12/04 13:02:53 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -618,12 +618,19 @@ pg_SSPI_continue(PGconn *conn)
 			return STATUS_ERROR;
 		}
 
+		/*
+		 * If the negotiation is complete, there may be zero bytes to send. The server is
+		 * at this point not expecting any more data, so don't send it.
+		 */
+		if (outbuf.pBuffers[0].cbBuffer > 0)
+		{
 			if (pqPacketSend(conn, 'p',
 					   outbuf.pBuffers[0].pvBuffer, outbuf.pBuffers[0].cbBuffer))
 			{
 				FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
 				return STATUS_ERROR;
 			}
+		}
 		FreeContextBuffer(outbuf.pBuffers[0].pvBuffer);
 	}