Items in the system don't stack with each other if 64 of the item already exists

[rythin-sr]

Assuming x + y < 64, inserting x of an item into the system and then later y of that same item will cause it to stack, making a single x+y stack. This only happens if there's <64 of said item already in the system. If a stack of 64 is already present, it will instead create two separate stacks of x and y respectively.

[MartinSVK12]

Fixed.