bug#60015: 29.0.60; multi-line messages truncated in non-selected minibuffer

[martin rudalics]

> Are you sure this is the reason and the possible fix?

It's neither.

> AFAICT, resize_echo_area_exactly doesn't get called in this scenario.
> Which might be part of the problem.

What I see is that

  if (!NILP (echo_area_buffer[0]) || minibuf_level == 0)

evaluates to false in echo_area_display.  So the problem seems to be
with 'set-message-functions' and there I'm lost.

martin