RFR: Fix refreshing of existing seeded folder

[Robin Westberg]

When a potentially stale materialization is used, we must ensure that the seed is still refreshed periodically.

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Commit messages:
 - Fix refreshing of existing seeded folder

Changes: https://git.openjdk.java.net/skara/pull/924/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=924&range=00
  Stats: 33 lines in 1 file changed: 3 ins; 15 del; 15 mod
  Patch: https://git.openjdk.java.net/skara/pull/924.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/924/head:pull/924

PR: https://git.openjdk.java.net/skara/pull/924