dix: only reject active grabs on ungrab and do it before actually ungrabbing

dix: only reject active grabs on ungrab and do it before actually ungrabbing

An active grab ungrabbing is the same as rejecting the grab, since the
client is no longer interested in those events. So reject any touch grab,
but do so before actually deactivating since we're interested in the
TouchEnd for the current grabbing client.

A passive grab otoh is _not_ like rejecting a grab, since it deactivates
automatically when the touch ends.

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