Crashes when unplugging wacom tablets (GTK3/Wayland/Firefox)

There's a number of Firefox crashes that seem to be related to unplugging Wacom tablets and look like they happen in GTK, specificly in tablet_pad_handle_leave. They have been observed with GTK versions that already include e.g. !1121 (merged)

See https://bugzilla.mozilla.org/show_bug.cgi?id=1631334

cc: @carlosg