fix(magnification): don't crash when reciving unexpected motion events.

This fixes an issue where the device was crashing and rebooting when
triple tapping to activate magnification at the same time as covering
the proxmity sensor while on a voice call.

Bug: b/236875528

Test: manual:
1. Perform a voice call
2. While on voice call, execute the "Triple tap on screen" gesture,
holding down your finger on the last tap and then cover the proximity
sensor.
3. The device should not crash

Change-Id: I9415c5b378b32342c016b17dfcef12cde45ce237