RFR: Avoid storing empty files

[Robin Westberg]

There should not be any need to push empty files to RepositoryStorage.

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Commit messages:
 - Avoid storing empty files

Changes: https://git.openjdk.java.net/skara/pull/893/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=893&range=00
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/893.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/893/head:pull/893

PR: https://git.openjdk.java.net/skara/pull/893