RFR: 8294717: (bf) DirectByteBuffer constructor will leak if allocating Deallocator or Cleaner fails with OOME [v2]

[Brian Burkhalter]

> Catch any `Throwable` from the `Deallocator` constructor or `Cleaner::create` and free memory to prevent a leak.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8294717: Add Bits.unreserveMemory to leak prevention

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10588/files
  - new: https://git.openjdk.org/jdk/pull/10588/files/03b92348..78e83b4f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10588&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10588&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10588.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10588/head:pull/10588

PR: https://git.openjdk.org/jdk/pull/10588