RFR: 8255248: NullPointerException in JFXPanel due to race condition in HostContainer [v5]

[Prasanta Sadhukhan]

> NPE is seen while accessing transient "scenePeer" variable between reads..
> Fix is made to store it in a temp variable rather than reading it twice since the value can change between successive reads in many places it is accessed.
> Also some debug logs added to be enabled via `jfxpanel.debug` property

Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:

  temp-var handling in few other methods

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1968/files
  - new: https://git.openjdk.org/jfx/pull/1968/files/7bf8a91e..fc830a7e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1968&range=04
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1968&range=03-04

  Stats: 70 lines in 1 file changed: 58 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jfx/pull/1968.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1968/head:pull/1968

PR: https://git.openjdk.org/jfx/pull/1968