RFR: forge: better metadata parsing for GitLab patches

[Erik Helin]

Hi all,

please review this patch that makes the metadata parsing for diffs from GitLab more robust.

Thanks,
Erik

-------------

Commit messages:
 - forge: better metadata parsing for GitLab patches

Changes: https://git.openjdk.java.net/skara/pull/920/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=920&range=00
  Stats: 23 lines in 1 file changed: 17 ins; 4 del; 2 mod
  Patch: https://git.openjdk.java.net/skara/pull/920.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/920/head:pull/920

PR: https://git.openjdk.java.net/skara/pull/920