TabRegistry - fix issues on returning to main inventory tab from another tab

Without this change, if you open the player's inventory, click to the Tinker's Construct inventory tab, then click _back_ to the vanilla inventory tab, any changes then made to the player inventory (e.g. crafting, or moving an item from a slot to a different slot) do not register on the server.

For further info please see the issue reported here https://github.com/micdoodle8/Galacticraft/issues/782
I hope you already knew we are making use of your TabRegistry code for Galacticraft's inventory tab as well - for compatibility reasons :)
Merge pull request #823 from radfast/master

TabRegistry - fix issues on switching back to vanilla inventory tab from TConstruct tab