Problem: buffer-listener callbacks may not match buffer content, since
they are buffered until the screen is updated.
Solution: Allow to handle buffer-callbacks un-buffered, meaning to
handle those changes as soon as they happen (Paul Ollis).
fixes: #18183closes: #18295
Signed-off-by: Paul Ollis <paul@cleversheep.org>
Signed-off-by: Christian Brabandt <cb@256bit.org>