RFR (S): 8072588 - JVM crashes in JNI if toString is declared as an interface method

[Andreas Eriksson]

Hi,

Please review this fix for a JNI issue in jni_invoke_nonstatic.

The problem is that when toString is declared as an interface method it 
still has a vtable index, not an itable index as jni_invoke_nonstatic 
expects.

This fix checks for a valid itable index instead of checking if the 
holder is an interface.
I also moved a duplicated check for JNI_VIRTUAL to be done in one check 
instead.
The change has been verified to fix the problem with a small JNI test, 
and has passed a jprt run with the hotspot testset.

Webrev:
http://cr.openjdk.java.net/~aeriksso/8072588/webrev.00/

Regards,
Andreas