submodule: fix latent check_has_commit() bug
When check_has_commit() is called on a missing submodule, initialization of the struct repository fails, but it attempts to clear the struct anyway (which is a fatal error). This bug is masked by its only caller, submodule_has_commits(), first calling add_submodule_odb(). The latter fails if the submodule does not exist, making submodule_has_commits() exit early and not invoke check_has_commit(). Fix this bug, and because calling add_submodule_odb() is no longer necessary as of 13a2f620b2 (submodule: pass repo to check_has_commit(), 2021-10-08), remove that call too. This is the last caller of add_submodule_odb(), so remove that function. (Submodule ODBs are still added as alternates via add_submodule_odb_by_path().) Signed-off-by: Glen Choo <chooglen@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>