Fix uninitialized repeat count in key events

A new "repeat" field has been added by
3c1ed5d86c38bcbd5353b0a7e6ef5653d6c44d0d, but it was not initialized in
every code path.

As a consequence, keycodes generated by shortcuts were sent with an
undetermined value, breaking some shortcuts (especially HOME) randomly.

Fixes #1643 <https://github.com/Genymobile/scrcpy/issues/1643>