bug#38466: 26.3; Gnus setting large-newsgroup-initial to "All"/nil defaults to gnus-large-newsgroup if display is set to all

[Allen Li]

Setting the group parameter large-newsgroup-initial to nil (meaning
"All") makes the default number of articles to show when prompted to be
the max, when there are more articles than gnus-large-newsgroup.

However, the default is equal to gnus-large-newsgroup if the group
parameter display is also set to all.

This is annoying when viewing nnimap groups where I want to show all
messages by default.  Due to the way group size estimation works by
subtracting min/max article numbers, the estimate for nnimap groups is
often very inflated, so I am almost always prompted to enter the number
of articles to show, which defaults to gnus-large-newsgroup rather than
the max.

I don't want to disable gnus-large-newsgroup entirely since it's useful
for actual newsgroups.

In GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.10)
 of 2019-08-29 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.12006000
System Description:     Arch Linux