[RFR] 8209191: [macOS] Distorted complex text rendering

[Arunprasad Rajkumar]

Hi Kevin,Phil,

Please review the fix for following bug,

https://bugs.openjdk.java.net/browse/JDK-8209191

Root cause:

JDK-8198354 takes care of NULL return from CTRunGetGlyphsPtr, the similar treatment has to be given for CTRunGetPositionsPtr[1] as well. 

(CTRunGetStringIndicesPtr already got that treatment). 

Webrev:

http://cr.openjdk.java.net/~arajkumar/8209191/webrev.01

[1] https://developer.apple.com/documentation/coretext/1510044-ctrungetpositionsptr?language=objc

Thanks,
Arun