Improve command execution with strange file names.

[Ryooooooga]

Fixed a problem where some commands would fail if the file name contained spaces, ", or multibyte characters (without git config core.quotePath false).

related: #378

• " in a filename (left: PR, right: master)

• then, when we type space, git add ... will fail (master)

• a filename starting with - (left: PR, right: master)

• multibyte characters (left: PR, right: master)

• in history (left: PR, right: master)

[jesseduffield]

tested locally and works like a charm. Nice work @Ryooooooga !