Incendiary grenades explode without fire

[TimGoll]

This seems to be an issue in v0.12.x and v0.13.x. Maybe even earlier. At least from what I heard, it is to confirm if this issue existed before #1318.

When fire grenades explode next to a wall, they always spawn their fire particles behind the wall. This is confusing when there is a room next to it, but outright buggy, if there is nothing behind it because it makes the particles spawn really far out triggering the crazy physics tool that removes them completely.