faces/simple_clock: clear segments if not in 024h

faces/simple_clock: clear segments if not in 024h

There was an issue where the simple clock's display would remain in
024h mode even after switching back to 12h/24h mode because it only
took into account the leading zero bit, whose value is meaningless
unless the 24h mode bit is also set.

The issue is fixed by taking both bits into account.

Closes #476.

Reported-by: CarpeNoctem <cryptomax@pm.me>
GitHub-Issue: https://github.com/joeycastillo/Sensor-Watch/issues/476