git-submodule - Fix errors regarding resolve_relative_url

git-submodule - Fix errors regarding resolve_relative_url

git-submodule was invoking "die" from within resolve-relative-url, but
this does not actually cause the script to exit. Fix this by returning
the error to the caller and have the caller exit.

While we're at it, clean up the quoting on invocation of
resolve_relative_url as it was wrong.

Signed-off-by: Mark Levedahl <redacted>
Signed-off-by: Junio C Hamano <redacted>