Fix incorrect file name on new or deleted empty files

[Patrick-Beuks]

The diff parser incorrectly parsed the below two diff patches

New file:

diff --git a/test b/test
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391

Deleted file:

diff --git a/test b/test
deleted file mode 100644
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..0000000000000000000000000000000000000000

As the diff file would incorrectly leave the newName/oldName in the diff fille. Breaking the isCreation(), isDeletion() and related functions as it would still contain a file name.

This PR fixes this by setting the file name to /dev/null when it is a new/deleted file.