RFR: defpath: catch errors when creating a Forge

[Erik Helin]

Hi all,

please review this patch that catches more errors in `git-defpath` when trying to create a `Forge` instance.

Thanks,
Erik

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Commit messages:
 - defpath: catch errors when creating a Forge

Changes: https://git.openjdk.java.net/skara/pull/770/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=770&range=00
  Stats: 20 lines in 1 file changed: 10 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/skara/pull/770.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/770/head:pull/770

PR: https://git.openjdk.java.net/skara/pull/770