Add "inside" as a prerequisite for insect spawn.

[yannisk]

For those of us who don't like building our base inside mountains, it can become frustrating having to deal with insects just because we mine resources for minerals or stone. Yes, you can cover the area with walls but that looks ugly and unnatural.

Can we do sth about this? So that we don't get penalised.

I cannot think of a way that someone could exploit this, unless they have no doors whatsoever in their base.