Blender Git Loki

When there are not associated button events, assume there is no button
events until one is found. This prevents errant cursor moves that occur
before the Wintab button event is reported. We need to skip these events
because if no button event exists, we generate one assuming it will either
arrive later in the Wintab queue or that the button was from a non-Wintab
device. For the case that this was generated by a non-wintab device, such
as buttons mapped to mouse on the tablet pad, these cursor move events can
significantly move the cursor from the intended click position.

Signed-off-by: Nicholas Rishel <rishel.nick@gmail.com>