Problem:
Giving a window a status line when `'laststatus'` starts requiring one
takes the row from a resizable frame found by walking up the frame
tree, but only the window's own leaf frame is grown back. Every frame
between the leaf and the donor keeps its old height, so a later resize
hands out a row that does not exist and a window's status line ends up
on the command line.
Solution:
Grow the window's frame with `frame_setheight()`, which takes the row
from a neighbouring frame and keeps every enclosing frame consistent.
3a39646693