RFR: Register filler objects when non-lab allocations are backed out

[William Kemper]

This is fallout from a recent change to have non-lab allocations stop registering objects. The code path for failed evacuations was not updated to register the filler objects created when the non-lab evacuation fails.

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Commit messages:
 - Register filler objects when non-lab allocations are backed out

Changes: https://git.openjdk.java.net/shenandoah/pull/86/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=86&range=00
  Stats: 15 lines in 1 file changed: 6 ins; 3 del; 6 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/86.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/86/head:pull/86

PR: https://git.openjdk.java.net/shenandoah/pull/86