JS: Channel Mapper-Downmixer can't undo mapping

[a.zhendi]

I can't clear mapping by clicking on already active (black) cell in the routing matrix.

Steps to reproduce the bug:
1) Click on any empty cell in the matrix.
2) Clicked cell should become active (black).
3) Click on this cell again to clear/deactivate it.

Actual behavior:
The cell stays in active/black mode and does not clears/deactivates.

Expected behaviour:
The cell should be clear and mapping should be deactivated.

System info:
macOS Monterey v 12.0
MacBook Pro (16-inch, 2021)
Apple M1 Pro
Reaper v6.42 / macOS-arm64 rev a8044b

Related small feature request:
Guys, please, add something like exclusive or solo mode for this plugin.
Like ctrl-click or shift-click on any empty cell activates it and clears all other cells.
It will be super handy, especially when working on surround material, to be able to instantly switch between channels for monitoring purposes.