Fix inner class access flags

[mrjameshamilton]

The inner class access flags are currently parsed using the expectClassAccessFlags method which parses the class access flags. The set of access flags allowed on the inner class is smaller than the class access flags (see https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.6-300-D.2-5).

In particular, the ACC_SUPER should not appear. JVMs appear to ignore this but stricter tools like ASM's CheckClassAdapter fail as the flags are invalid.

The error can be reproduced in the following small sample program that creates a Inner class file using the current ProGuard assembler release (1.0.0) and then tries to use the CheckClassAdapter from ASM on this class:

$ mvn compile
$ mvn exec:java -Dexec.mainClass="CreateBadClass"
...
Created BadOuter.class using proguard-assembler
Validation failed: Invalid access flags: 33

inner-class-validator.zip

[piazzesiNiccolo-GS]

Thanks for the repro sample, verified it fixes it 🎉