[Rev 03] RFR: 8236912: NullPointerException when clicking in WebView with Button 4 or Button 5

[Robert Lichtenberger]

> As documented in JDK-8236912, WebView did not check whether the idMap really contained a mapping for the given button, making it prone to errors, when things are extended (as has happened here).
> 
> The fix consists of two test cases that show the problem in unfixed WebViews and a fix which works analogously to the check whether the given event type is mapped.

Previous commits in this pull request have been removed, probably due to a force push. The incremental views will show differences compared to the previous content of the PR.

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Added commits:
 - aa03cf1f: Fix null pointer exception when clicking into WebViews with forward/back mouse button.

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/85/files
  - new: https://git.openjdk.java.net/jfx/pull/85/files/8c3f6017..aa03cf1f

Webrevs:
 - full: https://webrevs.openjdk.java.net/jfx/85/webrev.03
 - incr: https://webrevs.openjdk.java.net/jfx/85/webrev.02-03

  Stats: 187 lines in 4 files changed: 0 ins; 183 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/85.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/85/head:pull/85

PR: https://git.openjdk.java.net/jfx/pull/85