virtio/console: Fixed libkrun panic caused by console resizing during VM startup

[ihexon]

when vm booting, and console resize happened, libkrun crash immediately:

thread '<unnamed>' (2610281) panicked at src/devices/src/virtio/console/event_handler.rs:115:44:index out of bounds: the len is 0 but the index is 2
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Before this fix, process() read self.queue_events[CONTROL_RXQ_INDEX] and self.queue_events[CONTROL_TXQ_INDEX] before checking self.is_activated().

If a spurious pre-activation event arrived(says console resize), queue_events was still empty and the handler could panic with an out-of-bounds index.