D17537: Unset touch targets on no current touch points

romangg created this revision.
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REVISION SUMMARY
  Certain input devices like touch screens can be in a state of having no input
  target at all. In case of touch screens when there are no current touch points.
  
  In this case unset and block at-surface targets until a touch point is
  available again.

TEST PLAN
  Auto test window-selection passes again.

REPOSITORY
  R108 KWin

BRANCH
  touchCancelFix

REVISION DETAIL
  https://phabricator.kde.org/D17537

AFFECTED FILES
  input.cpp
  input.h
  touch_input.cpp
  touch_input.h

To: romangg, #kwin
Cc: kwin, mkulinski, ragreen, jackyalcine, Pitel, iodelay, bwowk, ZrenBot, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol, mart