RFR: 2495: Touch Command should return early on closed pull requests

[Zhao Song]

In [SKARA-2480](https://bugs.openjdk.org/browse/SKARA-2480), I added a new pull request command /touch. When the /touch command is issued on a closed pull request, Skara should return immediately. I forgot to add the return statement in that logic.

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Commit messages:
 - SKARA-2495

Changes: https://git.openjdk.org/skara/pull/1718/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1718&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2495
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1718.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1718/head:pull/1718

PR: https://git.openjdk.org/skara/pull/1718