Reset the expose cycle when polishAndSync aborts.

On platforms with misbehaving expose behavior, we will get
and exposure, even though the window is not renderable.
This results in the renderthread being in the "wait for polish"
state while the GUI thread goes back to "no state". Check
for this and reset render thread's expose cycle when it
is hit.

Task-number: QTBUG-37201

Change-Id: I6a6c89d9016301ff19443f88a2c182012b4eb65f
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>