[OpenJDK 2D-Dev] RFR: 8172967: [macosx] Exception while working with layout for text containing unmappable character

[Philip Race]

http://cr.openjdk.java.net/~prr/8172967/
https://bugs.openjdk.java.net/browse/JDK-8172967

Full evaluation in the bug report.
Short summary: avoid AIOB and NPE when Mac glyph mapper returns
a negated unicode which is misinterpreted as having composite font slot 255

-phil.