Looks like most of `ui_apply_but_XXX` or `ui_do_but_XXX` functions rely
on `uiHandleButtonData` (and not necessarily context).
Now the problem from a popover in `ui_but_list_row_text_activate` was
that the label button to be set in BUTTON_ACTIVATE_TEXT_EDITING for
renaming could not be found because it was using the "wrong" region from
context (`CTX_wm_region` - which still seem to point to the region the
popover was spawned from). The correct region is available in
`uiHandleButtonData` though, so now use this instead.
Not totally sure if `CTX_wm_region` should actually be correct in all
cases - which would hint at an underlying problem of not setting it
right - but since other functions rely on `uiHandleButtonData` as well,
this fix seems to make sense.
Fix should go into LTS I think.
