Git traverse fails with exception on missing directory

When running with the --git-repository flag the processing stops when a folder is missing within a commit, since the Finder component is throwing an InvalidArgumentException.

Use case:
```phploc --log-csv log.csv --progress --count-tests --git-repository . src ``` produces

```[InvalidArgumentException]  The "/path/to/src" directory does not exist. ``` when the src folder was removed within a revision, and added later on.