RFR: Following abbreviated cycle, only increment region age if aging cycle

[Kelvin Nilsen]

The previously existing code that processes regions following completion of an abbreviated cycle unconditionally
increased the age of all regions that had not allocated memory during the cycle.  It should only increment age of
regions if this is an aging cycle.  This patch fixes this behavior.

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Commit messages:
 - Following abbreviated cycle, only increment region age if aging cycle

Changes: https://git.openjdk.org/shenandoah/pull/214/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=214&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/214.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah pull/214/head:pull/214

PR: https://git.openjdk.org/shenandoah/pull/214