Correctly manage execution of invalid models

[gitgabrio]

Inside

DMNFEELHelper#compileFeelExpression(DMNCompilerContext, String, DMNModelImpl, DMNElement, Msg.Message, Object...) {
...
        CompiledExpression ce = feel.compile( expression, feelctx );
        processEvents( model, element, errorMsg, msgParams );
        return ce;
}

a CompiledExpression is returned even in presence of Syntax errors, that are simply sent to MsgUtil.
Then, the calling code

DMNEvaluatorCompiler#compileLiteralExpression(DMNCompilerContext, DMNModelImpl, DMNBaseNode, String, LiteralExpression) {
...
CompiledExpression compiledExpression = ctx.getFeelHelper().compileFeelExpression(ctx,
                                                                                        exprText,
                                                                                        model,
                                                                                        expression,
                                                                                    Msg.ERR_COMPILING_FEEL_EXPR_FOR_NAME_ON_NODE,
                                                                                        exprText,
                                                                                        exprName,
                                                                                        node.getIdentifierString() );
                    evaluator = new DMNLiteralExpressionEvaluator(compiledExpression, expression, ctx.getFeelHelper().newFEELInstance());
...

ignores the error messages, set the evaluator, and uses it to evalute the model.
The result of all that is inconsistent, since

1. on one side, the expression has syntax errors, so it should be completely discarded
2. but on the other side, an evaluator is instantiated and fired, leading to some kind of result.

This is demonstrated by the attached DMN-Invalid.txt