RFR: 8327370: (ch) sun.nio.ch.Poller.register throws AssertionError [v2]

[Daniel Fuchs]

> Please find here an almost trivial change that fixes an intermittent AssertionError observed in `sun.nio.ch.Poller`.
> 
> This change (in the mist of a bigger fix) was contributed by @AlanBateman to the loom repo two weeks ago.

Daniel Fuchs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8327370
 - Fix mistake - catch Throwable to cover more cases
 - 8327370

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19792/files
  - new: https://git.openjdk.org/jdk/pull/19792/files/33ed2820..1616b323

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19792&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19792&range=00-01

  Stats: 12211 lines in 64 files changed: 10322 ins; 958 del; 931 mod
  Patch: https://git.openjdk.org/jdk/pull/19792.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19792/head:pull/19792

PR: https://git.openjdk.org/jdk/pull/19792