RFR: 8373411: Crash when PrintSharedArchiveAndExit is enabled but shared heap is disabled [v2]

[Stefan Karlsson]

> Found this while poking around at Valhalla that turned off heap sharing. The fix is simple, there's a missing HeapShared::is_loading() check that we missed when refactoring the object streaming code.

Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:

  Review

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28741/files
  - new: https://git.openjdk.org/jdk/pull/28741/files/4221e141..a1dde921

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28741&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28741&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28741.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28741/head:pull/28741

PR: https://git.openjdk.org/jdk/pull/28741