Fix unknown Monster Family crashing the server (see #5442)

[tonitch]

Should solve #5442
I'm sorry for the other pr, I just messed it up so I make a new one...

Fixes #5442

[12xx12]

Thank You!

Just one minor comment.

[12xx12]

This won't crash. Good to merge

[tigerw]

Will this work if you pass -2? i.e. I think the problem is Lua calling C++ with arbitrary integer values but C++ not expecting them since it works based off the fixed set of enumeration values. I would suggest writing a manual binding similar to this and adding a manual error check like so:

cuberite/src/Bindings/ManualBindings_World.cpp

Lines 962 to 965 in 3b2a501

	if (!cChunkDef::IsValidHeight(Position))
	{
	return cManualBindings::lua_do_error(tolua_S, "Error in function call '#funcname#': Invalid 'position'");
	}

to cleanly report to the plugin that it did something wrong.

Something like if pluginmonstertype < mtInvalidType || pluginmonstertype > zombievillager { error } else { call cMonster::FamilyFromType(pluginmonstertype) }