RFR JDK-8193325: StackFrameInfo::getByteCodeIndex returns wrong value if bci > 32767

[Mandy Chung]

Having a second thought, I'm keeping @Stable bci field while zero 
indicates an invalid BCI that makes it obvious that this field will be 
updated.  VM will set StackFrameInfo::bci to value+1.

http://cr.openjdk.java.net/~mchung/jdk14/8193325/webrev.03/

Mandy