Bug ID: 104939
Summary: Tablet tools without ABS_Z cause a crash when updating
This affects tablets that are not listed in libwacom, specifically, tablets
where libwacom does not provide the stylus axis information.
On tablet init, we check the event codes. A tablet may have ABS_Z and thus have
rotation. Or it has BTN_TOOL_MOUSE + ABS_TILT_X/Y and thus have rotation. On
init, all axes are marked as 'changed' to ensure we send the data in the first
event. For non-libwacom tablets, the tool has the same bits set as the tablet
provides, so if mouse+tilt is there, we have rotation on all tools. But the
code itself relies on ABS_Z for rotation on all the styli (except mouse/lense).
In the case of Aiptek tablets we do have mouse+tilt but we *don't* have ABS_Z.
If the first tool that comes into proximity is *not* the mouse/lens tool ,
we try to update the rotation by accessing ABS_Z. This leads to a null-pointer
dereference in tablet_update_artpen_rotation() on the very first event.
It doesn't matter that the tool never sends the actual events - because all
axes are marked as 'changed' on proximity in, we always access the axis on the
first event and crash.
 see also Bug 104911
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