RFR: 8375070: NPE in Scene.ClickGenerator::preProcess when mouse button is none [v4]

[Christopher Schnick]

> A straightforward fix to just include MouseButton.NONE in the click counter map in cases weird mouse button events are sent. Alternatively, these events could also be ignored/dropped at some point

Christopher Schnick has updated the pull request incrementally with one additional commit since the last revision:

  Add test

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Changes:
  - all: https://git.openjdk.org/jfx/pull/2034/files
  - new: https://git.openjdk.org/jfx/pull/2034/files/836b88eb..8735a4e9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=2034&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=2034&range=02-03

  Stats: 11 lines in 1 file changed: 11 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/2034.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2034/head:pull/2034

PR: https://git.openjdk.org/jfx/pull/2034