Issue Description:

Any backpacks from Iron Backpacks can be put inside each other using Shift-Click.

What happens:

One backpack goes inside another. Other ways of doing this are banned.

What you expected to happen:

One backpack not going inside another backpack.

Steps to reproduce (important):

1. Get 2 backpacks in inventory.
2. Open 1 backpack.
3. Quick-move (Shift+LMB) other backpack.

Affected Versions (Do not use "latest"):

• IronBackpacks: 3.0.8-12
• Minecraft: 1.12.2
• Forge: 14.23.3.2669
• Other Conflicting Mods (may be irrelevant to your issue): Irrelevant

Screenshot

I can replicate this. I think we just need to check for the clicktype of QUICK_MOVE in ContainerBackpack.canTake and test the slot stack to see if it is an IBackpack

Will the next version ever be uploaded to curse? I just downloaded the latest beta and it still lets you shift them inside backpacks.