Gathers files on submodule recursive. And fixed the issue that occurs when multiple submodules contains.

[karupanerura]

Isses:

• Could not solve the recursive submodule.
• Outputting the incorrect results when multiple submodules contains.

Solutions:

• Gathers files on submodule recursive.
• Fix to required format when multiple submodules contains.

git ls-files -z does NOT print new line in last. So it breaks format when multiple submodules contains and combined with git submodule foreach. (and failed to parse.)