RFR of 8074819: Resolve disabled warnings for libzip

[Xueming Shen]

Hi,

Please help review the change to resolve the disabled "parentheses" warnings 
for libzip

issue: https://bugs.openjdk.java.net/browse/JDK-8074819
webrev: http://cr.openjdk.java.net/~sherman/8074819

thanks,
Sherman