RFR: JDK-8230776: Javac throws AssertionError in jvm.Gen.visitExec

[Vicente Romero]

Please review fix for [1] at [2]. The fix is ending the compilation at 
the code generation phase if a statement cant be generated and there is 
no way for the compilation to continue.

Thanks,
Vicente

[1] https://bugs.openjdk.java.net/browse/JDK-8230776
[2] http://cr.openjdk.java.net/~vromero/8230776/webrev.00/