RFR: webrev: add logging

[Erik Helin]

Hi all,

please review this small patch that add some additional logging to `Webrev` and dereferences `Optional`s a bit more
carefully in `ModifiedFileView`.

Testing:
- [x] `make test` passes on Linux x64

Thanks,
Erik

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Commit messages:
 - webrev: add logging

Changes: https://git.openjdk.java.net/skara/pull/674/files
 Webrev: https://webrevs.openjdk.java.net/skara/674/webrev.00
  Stats: 32 lines in 3 files changed: 15 ins; 0 del; 17 mod
  Patch: https://git.openjdk.java.net/skara/pull/674.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/674/head:pull/674

PR: https://git.openjdk.java.net/skara/pull/674