bug#73022: 31.0.50; Crash in build_frame_matrix_from_leaf_window after C-x 2 and reducing terminal size

[Bug reports for GNU Emacs, the Swiss army knife of text editors]

> I don't think it's an off-by-one.  It's simply that Emacs draws the
> screen top to bottom, so the very first row that violates the
> assertion by exceeding FrameRows is the only one that is seen.

You're right.

martin