RTL node-contents width is too long

[derekstory]

This is for Impact issue: https://github.com/SpiderStrategies/Scoreboard/issues/59844

This is subtracting a negative value but the value should be positive to fit the space:

So that overflows which is why the code makes it expand:

This was caused by a change I made:

https://github.com/SpiderStrategies/kalpa-tree/commit/4f6c953b0f737a190e3131bcff66d8ee0ad7e5ac