Blender Git Loki

UI: fix buttons ranges not properly updated when tabbing to next/previous
button

This was reported for the FCurve modifier restrict ranges, but might fail
elsewhere, too. Reason is that the post_but has its range (hardmin/
hardmax etc) set before the updates to the active button take place, so
changes here dont end up on the post_but (even though the RNA range
function is properly called for a new defined button - new one is not the
same as the post_but though).

Now update the ranges on the post_but when that gets active.

Fixes T78763

Maniphest Tasks: T78763

Differential Revision: https://developer.blender.org/D8265