Fix error with redundant line breaks

[pfeuffer]

Proposed changes

This fixes an error with a repository, where an added file has \r\r\n
as line breaks. This interesting combination is handled as a single
line break by the diff operation, while Java's Scanner implementation
handles this as two lines (the first one delimited by the first \r,
the second one delimited by \r\n. This led to empty lines inside the
diff, where we only expect lines that contain at least one character
(' ', '+' or '-'), and this in turn led to an index out of bounds
exception.

Now we handle each combination of any kind of new line delimiter
characters as a single delimiter. This should be safe, because, as
mentioned earlier, we always expect at least one character in a line
for a diff output.

Your checklist for this pull request

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• PR is well described
• Target branch is not master (in most cases develop should bet the target of choice)
• Code does not conflict with target branch
• New code is covered with unit tests
• CHANGELOG.md updated
• Documentation updated (only necessary for new features or changed behaviour)

Checklist for branch merge request (not required for forks)

• Branch is green/blue on Jenkins
• Quality Gate passed on SonarQube