`winfixheight` is a hint, not a rule. When the tabline disappears and
nvim has to put the reclaimed row SOMEWHERE, it can shove it into one
of our bars, growing it to 3 rows. Our buffer only has 2 lines, so
the 3rd row renders `~` — the stray EOB line the user saw between
the cbar's bottom sep and the lualine statusline.
Previously `ensure_bar_heights()` only corrected shrinkage (`< 2`).
Now it clamps in both directions (`~= 2`). When we shrink an over-
sized bar, the freed row has to go somewhere — the WinResized path's
pin_dapui_sizes() redistributes it across dapui panes proportionally.
swaits
8fbccb9391