Blender Git Loki

Fix T48204: Generic Tablet on Linux - Erratic strokes with pressure sensitivity enabled.

Once and for all - I hope!

So, for the records: Xinput1 events' valuators have a first_axis and axis_count defining the 'range'
of valid axes for that event - but valid data in the valuator's array **always** start at zero
(which means that, if event reports first axis as being axis 2, axis 2's value is in axis_data[0]).