sidebar: tab_bar_pad back to 0, now that the frame is the separation

The row of air was standing in for a boundary the sidebar did not have.
tab_bar_chrome gave it one, and a blank row inside the frame on top of
that reads as a gap nobody asked for. The knob stays for a bare sidebar
(tab_bar_chrome false), and for anyone who wants room at the top for a
borderless window's own buttons.

With the default at 0, Y0 in the tests is the unpadded first row and a
pad of N moves the list exactly N rows down from it, which is what the
pad test now says rather than carrying the default around in its
arithmetic.

0 files changed, 0 insertions, 0 deletions