Merge branch 'jk/initialization-fix-to-add-submodule-odb'

We peek objects from submodule's object store by linking it to the
list of alternate object databases, but the code to do so forgot to
correctly initialize the list.

* jk/initialization-fix-to-add-submodule-odb:
add_submodule_odb: initialize alt_odb list earlier

diff --cc submodule.c
Simple merge