VariableBinder in lambda compiler does not analyze CatchBlock.Filter

[bartdesmet]

Repro:

var e =
    Expression.Lambda<Action>(
        Expression.TryCatch(
            Expression.Empty(),
            Expression.Catch(
                Expression.Parameter(typeof(Expression), "ex"),
                Expression.Empty(),
                Expression.Parameter(typeof(bool), "???")
            )
        )
    );
e.Compile();

This gets as far as ILGen (failing there for DynamicMethod emit due to a limitation in System.Reflection.Emit that's tracked to be lifted at some point, see https://github.com/dotnet/corefx/issues/3838). The culprit is the lack of recursion into the Filter child node of CatchBlock in VariableBinder.