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 "patchbomb=" >> $HGRCPATH
hg init
echo a > a
hg commit -Ama -d '1 0'
hg email --date '1970-1-1 0:1' -n -f quux -t foo -c bar tip | \
sed -e 's/\(Message-Id:.*@\).*/\1/'
echo b > b
hg commit -Amb -d '2 0'
hg email --date '1970-1-1 0:2' -n -f quux -t foo -c bar -s test 0:tip | \
sed -e 's/\(Message-Id:.*@\).*/\1/' | \
sed -e 's/\(In-Reply-To:.*@\).*/\1/'
hg email -m test.mbox -f quux -t foo -c bar -s test 0:tip