Fixed error when spawning non-mob entities in a peaceful world

[36451]

Added cavespiders to the peaceful blocklist
Resolves some errors from this thread:
https://forum.cuberite.org/thread-1828.html

[madmaxoft]

I wonder, why do you check Ent:IsMob() == true? If the it isn't a mob, it still has a GetClass() function, so the line inside the if will not cause any trouble, and in Lua you can use any index in a table, if the item doesn't exist, you get a nil (which is handled pretty much same as false in conditionals)

[madmaxoft]

Actually, this code is full of WTFs: why cast a cEntity object to a cEntity? (line 98). Also, if the cast failed somehow, the Ent variable would become nil and thus the condition on the next line will cause a runtime error in the script.

[36451]

The issue (as i understand it) seems to be that we sometimes get cExpBottleEntity / cArrowEntity instead of cEntity, and that causes some weird problems with Entity:GetClass().
And i added the ismob as an additional safeguard.

This might be a workaround instead of a bugfix.
Where bugfix could require modification to the server sourcecode.

[NiLSPACE]

But cExpBottleEntity and cArrowEntity are a cEntity, so that shouldn't be the problem.

[36451]

Seems so. Still,

 [15:21:46] LUA: Plugins/Core/difficulties.lua:98: error in function 'GetClass'.
     argument #1 is 'cExpBottleEntity'; 'const cEntity' expected.

[15:21:46] Stack trace:
[15:21:46]   [C](-1): GetClass
[15:21:46]   Plugins/Core/difficulties.lua(98): (no name)
[15:21:46] Stack trace end
[15:21:46] Error in plugin Core calling function <callback>()

[NiLSPACE]

That should only be a problem if you would have used tolua.type(Entity)

[madmaxoft]

I think there's a problem with how ToLua handles class inheritance and const functions. Definitely an API problem, though, not a Core one.

[36451]

I think we can leave this until the API is fixed.
In the meantime i'll start hunting for that particular bug.

[36451]

cExpOrb is an extension of the cEntity, whereas cArrow and cExpBottle are extensions of cProjectileEntity, which is extending cEntity.
(It works only for direct descendants?)