RFR: 8236484: Compile error in monocle dispman

[Johan Vos]

Trivial fix for a compiler error where a void function returns a long

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Commits:
 - 5c066016: Trivial fix for a compiler error where a void function returns a long

Changes: https://git.openjdk.java.net/jfx/pull/74/files
 Webrev: https://webrevs.openjdk.java.net/jfx/74/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8236484
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/74.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/74/head:pull/74

PR: https://git.openjdk.java.net/jfx/pull/74