Init genericMasks to 0, make sure list is NULL terminated.

Xi/exevents.c

@@ -1169,6 +1169,7 @@ CheckDeviceGrabAndHintWindow(WindowPtr pWin, int type,
 	tempGrab.pointerMode = GrabModeAsync;
 	tempGrab.confineTo = NullWindow;
 	tempGrab.cursor = NullCursor;
+        tempGrab.genericMasks = NULL;
 	(*dev->deviceGrab.ActivateGrab) (dev, &tempGrab, currentTime, TRUE);
     }
 }

dix/events.c

@@ -5912,6 +5912,7 @@ ExtGrabDevice(ClientPtr client,
             last->next = xcalloc(1, sizeof(GenericMaskRec));
             last = last->next;
             *last = *ge_masks;
+            last->next = NULL;
             ge_masks = ge_masks->next;
         }
     }