bugfix #309: broken step-in/step-over in eclipse

History Cannot Use Step Filters while Debugging in Eclipse #309
Fix PR315

Eclipse plugin is on low priority and it debugger there was working on simple cases year ago I was checking. Simple debug session discovered the bug in Event request validation.

Root case

Problem case there was validation of EXCEPTION_ONLY.referenceTypeID event modifier against list of known to debugger ones, but there is case when it can be zero:

referenceTypeID: exceptionOrNull. Exception to report. Null (0) means report exceptions of all types. A non-null type restricts the reported exception events to exceptions of the given type or any of its subtypes.

The fix is trivial:

                 case JdwpConsts.EventModifier.EXCEPTION_ONLY:
                     itemId = ((EventExceptionPredicate) predicate).refTypeId();
-                    if (delegates.state().classRefIdHolder().objectById(itemId) == null)
+                    if (itemId != 0 && delegates.state().classRefIdHolder().objectById(itemId) == null)
                         throw new DebuggerException(JdwpConsts.Error.INVALID_CLASS);
                     break;

Protocol version downgraded v1.6 -> v1.5

RoboVM doesn’t support bunch of capabilities of v1.6 but there are functionalities that can not be disabled in response to capabilities requests and has to be supported. And eclipse uses it. For example it actively uses METHOD_EXIT_WITH_RETURN_VALUE event kind on step-in/step-over filters.
JDPW version downgrade shall not affect debugger functionality as most of 1.6 features are not supported.