RFR: 8341015: OopStorage location decoder crashes accessing non-initalized OopStorage [v2]

[Aleksey Shipilev]

> When debugging CDS, I asked for `os::print_location` before OopStorage was initialized, like an error handler would do. This is a fairly unusual situation, this is why we have not seen it before. Anyhow, we entered the new code added by [JDK-8340392](https://bugs.openjdk.org/browse/JDK-8340392), which crashed on `OopStorage` that was `nullptr`. I think we should null-check `OopStorage` before calling into it.
> 
> Additional testing:
>  - [x] OopStorageSetTest still passing
>  - [x] Verified the check is now passing in similar debugging session

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Touchups

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21204/files
  - new: https://git.openjdk.org/jdk/pull/21204/files/c2e276c6..73b21b46

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21204&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21204&range=00-01

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21204.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21204/head:pull/21204

PR: https://git.openjdk.org/jdk/pull/21204