shell: Stop moving surfae after touch point 0 goes up

shell: Stop moving surfae after touch point 0 goes up

The grab stays alive as long as at least one touch point is down.  If touch
point 0 is lifted while other touch points are down, the surface will jump
around when touch point 0 is put down again.

This change marks the grab as inactive once touch point 0 is lifted
and then ignores touch events until all touch points eventually are
lifted and the grab terminates.

https://bugs.freedesktop.org/show_bug.cgi?id=73750