Fixed out-of-range memory accesses

[user40]

Accessing memory out of range, such as during a game restart, can fill the lua console with error messages and slow down the frame rate.
To avoid this I added a check of the address in advance before reading the memory.

[DevreeseJorik]

Would you mind also adding these checks for the Memory:write and GetByteRange methods? I can also do it myself. We can merge it once that's done.

[user40]

Okay, I'll do it.

[user40]

I Added boundary checks to Memory:write* and Memory:getByteRange*.
They also do nothing or return 0 for meaningless addresses. Do you prefer other error handles?