Merge branch 'rs/submodule-config-code-cleanup' into maint

Code cleanup.

* rs/submodule-config-code-cleanup:
  submodule-config: fix test binary crashing when no arguments given
  submodule-config: combine early return code into one goto
  submodule-config: passing name reference for .gitmodule blobs
  submodule-config: use explicit empty string instead of strbuf in config_from()

diff --cc submodule-config.c
Simple merge

diff --cc t/helper/test-submodule-config.c
Simple merge