RFR: JDK-8035930 - Check jdk/src/windows/native/java/io/io_util_md.c for JNI pending exceptions

[Mark Sheppard]

Hi
    please oblige and review the following changes
http://cr.openjdk.java.net/~msheppar/8035930/webrev/

to address the issues raised in
https://bugs.openjdk.java.net/browse/JDK-8035930

this adds additional NULL check for malloc and JNI calls
and check for pending exceptions as appropriate

regards
Mark