Merge branch 'rr/maint-submodule-unknown-cmd' into maint

"git submodule frotz" was not diagnosed as "frotz" being an unknown
subcommand to "git submodule"; the user instead got a complaint that
"git submodule status" was run with an unknown path "frotz".

* rr/maint-submodule-unknown-cmd:
  submodule: if $command was not matched, don't parse other args

diff --cc git-submodule.sh
Simple merge

diff --cc t/t7400-submodule-basic.sh
Simple merge