RFR: 8336389: Infinite loop occurs while resolving lookups [v7]

[John Hendrikx]

> Fixes an infinite loop that can occur while resolving lookups.
> 
> There were 2 bugs:
> - A `contains` check was done on some value X, but then a value Y was added to the set used to track duplicates
> - The `Set` to track duplicates was cleared in some recursive calls, meaning that the caller (which may be processing multiple values in a loop) would end up with an empty set, losing track of what was visited so far
> 
> Also removed a redundant `null` check (an NPE would have occurred before it could reach that code).

John Hendrikx has updated the pull request incrementally with one additional commit since the last revision:

  Update CssStyleHelper.java

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1505/files
  - new: https://git.openjdk.org/jfx/pull/1505/files/72d64b0f..ff5788c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1505&range=06
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1505&range=05-06

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1505.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1505/head:pull/1505

PR: https://git.openjdk.org/jfx/pull/1505