RFR (S) 8219577: Returning NULL in a function which returns bools

[Schmelter, Ralf]

Please review this change which replaces 2 'return NULL' with 'return false' in a method returning bools. Since this is in windows only code, the fix was only tested on windows.

webrev: http://cr.openjdk.java.net/~rschmelter/webrevs/8219577/webrev.0/
bug: https://bugs.openjdk.java.net/browse/JDK-8219577

Best regards,
Ralf