[2.46 regression] git ls-remote crash with import remote-helper

[Mike Hommey <mh@xxxxxxxxxxxx>]

Hi,

Running `git ls-remote $helper::$url` crashes when run outside a git
repo and the helper uses the import feature.

Here is a minimal reproducer:
```
$ cat > git-remote-foo <<EOF
#!/bin/sh
echo import
echo refspec '*:*'
EOF
$ chmod +x git-remote-foo
$ PATH=$PWD:$PATH git ls-remote foo::bar
```

The crash happens in parse_refspec in refspec.c, on a deref of the_hash_algo,
because the_hash_also is not set anymore at that point since c8aed5e8da.

Mike