git-submodule.sh: try harder to fetch a submodule

This is the logical continuum of fb43e31f2b4 (submodule: try harder to fetch needed sha1 by direct fetching sha1, 2016-02-23) and fixes it as some assumptions were not correct. The commit states: > If $sha1 was not part of the default fetch ... fail ourselves here > assumes that the fetch_in_submodule only fails when the serverside does > not support fetching by sha1. There are other failures, why such a fetch may fail, such as fatal: Couldn't find remote ref HEAD which can happen if the remote side doesn't advertise HEAD and we do not have a local fetch refspec. Not advertising HEAD is allowed by the protocol spec and would happen, if HEAD points at an unborn branch for example. Not having a local fetch refspec can happen when submodules are fetched shallowly, as then git-clone doesn't setup a fetch refspec. So do try even harder for a submodule by ignoring the exit code of the first fetch and rather relying on the following is_tip_reachable to see if we try fetching again. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>