bug#57669: 29.0.50; C-n, C-p off under long lines

[dick]

> A rather strange conclusion.

languageclient.out
Description: Text document

I'm standing by my underwhelming characterization.

C-n'ing through a real-world logfile languageclient.out, which I attach
again here, chops up at around line 44.  This led me to write contrived
tests, which of course are frowned upon in your school of measurement,
whose modus operandi is interminable catechism between a complainant who
laboriously and imprecisely describes slowness, and an inquisitor
auto-replying "doesn't happen here."

To your credit, underwhelming is far better than ineffable, so I've
largely been dismissive of the objections by the usual suspects in
Bug#56393.