[BUG] Opening a backpack from the main hand may perform off hand action.

[SlashLife]

Describe the bug
When opening a backpack from a backpack key in the main hand while an empty hand would have caused an off hand action, the off hand action is performed in addition to opening the backpack.

To Reproduce
Steps to reproduce the behavior:

1. Wear a backpack, hold the backpack key in the main hand and a torch in the off hand.
2. Stand next to a block that a torch can be placed on.
3. Right click the block with the backpack key.
   The backpack opens and a torch is placed.

Expected behavior
The backpack opens, but no torch is placed. (alike to e.g. book & quill)

Version info
Spigot 1.20.1 (3871)
Backpacks 2022.1.8

Additional context
May be related to #54