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