hg: openjfx/8u-dev/rt: Follow-up for RT-37006: add comment and thread check

[hang.vo at oracle.com]

Changeset: f943c6e121b7
Author:    kcr
Date:      2014-05-14 10:36 -0700
URL:       http://hg.openjdk.java.net/openjfx/8u-dev/rt/rev/f943c6e121b7

Follow-up for RT-37006: add comment and thread check

! modules/graphics/src/main/java/com/sun/javafx/tk/quantum/QuantumToolkit.java