discovery: only calculate closed branches if required
The number of new closed branches is required for printing in error message. So
let's only calculate them if we need to print error about new branches.
Differential Revision: https://phab.mercurial-scm.org/D6314
#require serve repobundlerepo
$ hg init server
$ cd server
$ cat >> .hg/hgrc << EOF
> [extensions]
> strip=
> EOF
$ echo 1 > foo
$ hg commit -A -m 'first'
adding foo
$ echo 2 > bar
$ hg commit -A -m 'second'
adding bar
Produce a bundle to use
$ hg strip -r 1
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
saved backup bundle to $TESTTMP/server/.hg/strip-backup/ed602e697e0f-cc9fff6a-backup.hg
Serve from a bundle file
$ hg serve -R .hg/strip-backup/ed602e697e0f-cc9fff6a-backup.hg -d -p $HGPORT --pid-file=hg.pid
$ cat hg.pid >> $DAEMON_PIDS
Ensure we're serving from the bundle
$ (get-with-headers.py localhost:$HGPORT 'file/tip/?style=raw')
200 Script output follows
-rw-r--r-- 2 bar
-rw-r--r-- 2 foo