Fix MSVC warnings in monster.cpp/monsterdat.cpp

[obligaron]

This PR reduces warnings by 20 (from 137 to 117)

[AJenbo]

Now I'm sitting here wondering if we should have made getId() return unit8_t 🤔

[obligaron]

Now I'm sitting here wondering if we should have made getId() return unit8_t 🤔

Yeah. It's a tricky one...

uint8_t could be a little bit too low, if we want to support more then 200 monsters.
Something larger would still need some casts (against size_t or int16_t for example in dMonster).

For now I use size_t until it gets stored in some structure that's also get saved or when doing network related stuff.