httppeer: avoid another bad reference before assignment warning
This wasn't a problem, because `b''` from the `AttributeError` handler is in
`bundle2.bundletypes`, so the following loop and conditional always run at least
once. But PyCharm can't figure that out on its own, and it took a little
exploring to figure out it wasn't a problem. The usage in `bundle2.writebundle`
is to look it up in the map of bundle types, so it will break in a more obvious
way in the unlikely event that the empty string is removed from the map in the
future.
$ hg init repo
$ cd repo
$ echo 0 > a
$ hg ci -qAm 0
$ for i in 5 8 14 43 167; do
> hg up -q 0
> echo $i > a
> hg ci -qm $i
> done
$ cat <<EOF >> .hg/hgrc
> [alias]
> l = log -T '{rev}:{shortest(node,1)}\n'
> EOF
$ hg l
5:00f
4:7ba5d
3:7ba57
2:72
1:9
0:b
$ cat <<EOF >> .hg/hgrc
> [experimental]
> revisions.disambiguatewithin=not 4
> EOF
$ hg l
5:00
4:7ba5d
3:7b
2:72
1:9
0:b
9 was unambiguous and still is
$ hg l -r 9
1:9
7 was ambiguous and still is
$ hg l -r 7
abort: ambiguous revision identifier: 7
[10]
7b is no longer ambiguous
$ hg l -r 7b
3:7b
$ cd ..