dix: reset potential lastSlaves when disabling an SD

Unplug a mouse, then warp the pointer and the warp pointer code will try
to update the position of the last slave device associated with the
master. That pointer will be stale and the X server will crash.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

dix/devices.c

@@ -358,6 +358,14 @@ DisableDevice(DeviceIntPtr dev)
                 AttachDevice(NULL, other, NULL);
         }
     }
+    else
+    {
+        for (other = inputInfo.devices; other; other = other->next)
+        {
+	    if (other->isMaster && other->u.lastSlave == dev)
+		other->u.lastSlave = NULL;
+	}
+    }
 
     if (dev->isMaster && dev->spriteInfo->sprite)
     {