fix 'convert' with single commit repositories
The attached patch passes the three 'convert' testcases, and also is
able to successfully convert the git.git repository.
#!/bin/sh
echo "[extensions]" >> $HGRCPATH
echo "mq=" >> $HGRCPATH
hg init a
cd a
echo 'base' > base
hg ci -Ambase -d '1 0'
hg qnew -mmqbase mqbase
hg qrename mqbase renamed
mkdir .hg/patches/foo
hg qrename renamed foo
hg qseries
ls .hg/patches/foo
mkdir .hg/patches/bar
hg qrename foo/renamed bar
hg qseries
ls .hg/patches/bar
hg qrename bar/renamed baz
hg qseries
ls .hg/patches/baz