RFR: 8264330: Scene MouseHandler is referencing removed nodes [v3]

[John Hendrikx]

> Small fix to clear a reference to a removed node left by Scene$MouseHandler.

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

  Add test compile dependency on :base for :graphics

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/448/files
  - new: https://git.openjdk.java.net/jfx/pull/448/files/371ede22..0be3b899

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=448&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=448&range=01-02

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/448.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/448/head:pull/448

PR: https://git.openjdk.java.net/jfx/pull/448