RFR(XS): -XX:+CITime triggers guarantee(events != NULL) in jvmci.cpp

[Schmidt, Lutz]

Dear all, 

may I please request reviews for this small fix? I would even say it is a trivial fix. It inverts an if condition such that JVMCI specific code is called only when JVMCI compilation is enabled via UseJVMCICompiler.

Bug:    https://bugs.openjdk.java.net/browse/JDK-8250233
Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8250233.00/ 

Local testing looks good. jdk/submit tests pending.

Thank you!
Lutz