BufferUtil - Fix off-by-one bug

[MrBlackbrow]

I noticed that BufferUtil has a size comparison that is < when it should be <=. The reason this mistake happened is probably because buffers are 0-indexed, unlike the rest of Lua.

The problem can be seen with the following example:

local writer = BufferUtil.writer(3)
print(writer:GetCapacity()) -- 3
writer:WriteUInt8(1)
writer:WriteUInt8(1)
writer:WriteUInt8(1)
print(writer:GetCapacity()) -- 4

In the example you can see that the buffer is created with size 3 and we write 3 bytes to it, but it gets expanded to 4 even though it's not necessary. Also important to note that the issue won't be apparent when writing a number of bytes that's a power of two, because the "expanded" size ends up being same as before.