If a touch is in TOUCH_NONE, there is nothing to see here, please move along.

In the case of bug 105696, we were accessing the speed.exceeded_count of a
touch that was released previously, erroneously detecting a speed-based thumb.
The sequence was:
- touch down in slot 0, speed.exceeded_count is reset to 0
- move touch until exceeded_count is greater than our threshold
- touch up in slot 0
- touch down in slot 1 [1]
- touch down in slot 2 (more than 25mm away)
- we counted the slot 0 speed.exceeded_count, labeling the slot 2 touch as
  speed-based thumb

[1] peculiar behavior only observed on this device, usually slots get re-used
at the first opportunity so having an inactive slot followed by higher slots
being used is unusual.

https://bugs.freedesktop.org/show_bug.cgi?id=105696



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