Fix file rename issues.

If filename is anything but a valid `Lang::createFilename()`, the algorithm fails to correctly rename duplicate files.

Example on current code:

    File #1: "foo bar.jpg"
    Does "path/to/images/foo bar.jpg" exist? No. Continue.
    Create file handle => "foo-bar.jpg"
    ...

    File #2: "foo bar.jpg"
    Does "path/to/images/foo bar.jpg" exist? No. Continue.
    Create file handle => "foo-bar.jpg"
    => file duplication not detected
    ...

Example with patched code:

    File #1: "foo bar.jpg"
    Create file handle => "foo-bar.jpg"
    Does "path/to/images/foo-bar.jpg" exist? No. Continue.
    ...

    File #2: "foo bar.jpg"
    Create file handle => "foo-bar.jpg"
    Does "path/to/images/foo-bar.jpg" exist? Yes. Run duplicate file algorithm. Continue.
    => file duplication fixed
    ...