test: check that the pressure offset is reduced during motion events too

test: check that the pressure offset is reduced during motion events too

Ensure that if we do get pressure < offset that that offset is reduced
to the current pressure value.

The implementation for this is arguably buggy, reducing the pressure
means we get a tip up event since we now reach 0% of pressure. Arguably
we should enforce the tip staying down and releasing it later but since
this should typically never happen more than once per tool per context
and working around this is a lot of effort, we live with it.

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