Zero out the ENGPACKET allocated on the stack, to avoid sending uninitialized

values to reserved fields on the card, resulting in all-black output and
sometimes hangs.

Submitted by:	Thomas Winischhofer

src/mesa/drivers/dri/sis/sis_screen.c

@@ -316,6 +316,8 @@ static void sisCopyBuffer( __DRIdrawablePrivate *dPriv )
    int i;
    ENGPACKET stEngPacket;
   
+   memset(&stEngPacket, 0, sizeof(ENGPACKET));
+
    while ((*smesa->FrameCountPtr) - MMIO_READ(0x8a2c) > SIS_MAX_FRAME_LENGTH)
       ;