test: abort when no default value is available for an axis

And fix the cases where the default value isn't filled in correctly

Issue found because of the following ubsan error:
../src/evdev-tablet.c:182:19: runtime error: signed integer overflow: 0 - -214783648 cannot be represented in type 'int'

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