Setting setFullScreen(true) on a modal stage effectively breaks the application.

This may or may not be related to JDK-8358620 Prevent iconification of a modal stage.

To reproduce using the monkey tester
https://github.com/andy-goryachev-oracle/MonkeyTest

- select Stage page
- configure Stage properties: modality=WINDOW_MODAL, set owner=(true or false), stage style = DECORATED
- press Show Stage button
- right click on the stage and select Full Screen

Expected: the operation is either ignored (be it's a modal?) or the window goes full screen
Observed: the app becomes partially unresponsive, closing the window with native toolbar and opening the test stage again shows a blank or black window