bug#25115: 26.0.50; ibuffer fails to show confirmation buffer when there are side windows

[martin rudalics]

> Your patch has perfect sense to me.  Indeed i wrote an almost identical
> fix but you were faster than me.

Damn.  Next time I'll wait a day or two :-(

But we still don't know what this ‘window-list’ stuff is all about.  I'd
rather have asked ‘walk-window-tree-1’ on the main window to return the
last window it sees, but consider the following emacs -Q scenario:

C-x 2
C-x o
M-x ibuffer
m
m
D

The confirmation buffer appears above the ibuffer buffer.  I doubt that
such behavior is intentional but since I'm no ibuffer user ...

martin