RFR: 1019: IssueNotifier fails if there are extra branches in a repo

[Erik Joelsson]

This change makes the notifier bot more lenient when finding branches without fixVersions configured, or when those fixVersions do not have backports in the issue tracker, when processing new tags. Currently either of these cases will cause the rest of the commits affected by a tag to never get processed. See bug for more details.

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Commit messages:
 - SKARA-1019

Changes: https://git.openjdk.java.net/skara/pull/1147/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1147&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1019
  Stats: 8 lines in 2 files changed: 5 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/skara/pull/1147.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1147/head:pull/1147

PR: https://git.openjdk.java.net/skara/pull/1147