Player Health may go negative

[thombruce]

A ludicrous experiment in spawning enemies on a timer brought this to my attention:

The player's health may go negative (e.g. taking multiple hits in the same tick) and the player will not despawn; there is effectively no game over.

[thombruce]

Turned out not to be a multiple-hit issue. I'd sensible already used a <= for ship death handling. Instead, the issue was a silent failure of the ship death handling in the case that no adversaries were found (as the player lacks this); I believe that's the case anyway, and so the despawn command was never reached.