RFR: 1292: Empty commit message causes IndexOutOfBoundsException

[Erik Joelsson]

This patch fixes an IndexOutOfBoundsException which occurs when a new repository is configured and it contains commits with an empty message. The message() here represents the commit message as a List<String> with one item for each line. If the message is empty, the list is empty. From what I can tell, returning an empty string in that case should work fine.

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Commit messages:
 - SKARA-1292

Changes: https://git.openjdk.java.net/skara/pull/1265/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1265&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-1292
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/1265.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1265/head:pull/1265

PR: https://git.openjdk.java.net/skara/pull/1265