Correct brace error that prevents explosions from damaging vehicles directly.

This is a 2nd channel for explosions to damage vehicles, but it was bugged by a brace placement error to only trigger if there was also a  monster on the square.
It either needs to be fixed like this, increasing damage to vehicles from explosions, or removed.
With some light testing lobbing 40mm grenades at some vehicles, the damage seemed quite low before, and better now, so I'm leaning toward this solution.