stream: in v3, skip the "size" fast path if the entries as some unknown size
We are about to prefetch size during the lock less in the v3 case. So we need to
avoid trying to use that prefetched size when it is not available.
See next changeset for the motivation.
$ hg init a
$ cd a
$ touch a; hg commit -qAm_
$ hg bookmark $(for i in $($TESTDIR/seq.py 0 20); do echo b$i; done)
$ hg clone . ../b -q
$ cd ../b
Checking that when lookup multiple bookmarks in one go, if one of them
fails (thus causing the sshpeer to be stopped), the errors from the
further lookups don't result in tracebacks.
$ hg pull -r b0 -r nosuchbookmark $(for i in $($TESTDIR/seq.py 1 20); do echo -r b$i; done) ssh://user@dummy/$(pwd)/../a
pulling from ssh://user@dummy/$TESTTMP/b/../a
abort: unknown revision 'nosuchbookmark'
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