Quickbar: Fixed creating a new stack pushing others off the quickbar

Picking up a block while not having a partial stack of it (a multiple of 64 or 0 of the item) was pushing all the other quickbar items down one (so, one disappears), this fixes that.

Made a new pull request to ensure a clean merge with the recent changes in the file, first PR was #4

Is there an IRC or something we could discuss this project in? irc://irc.gamesurge.net/Pinecraft perhaps?