Added missing bool query filter visit on QueryWalker

Author: jonyadamit

src/Nest/QueryDsl/Visitor/QueryWalker.cs

@@ -68,6 +68,7 @@ public void Walk(IQueryContainer qd, IQueryVisitor visitor)
 			VisitQuery(qd.Bool, visitor, (v, d) =>
 			{
 				v.Visit(d);
+				Accept(v, d.Filter, VisitorScope.Filter);
 				Accept(v, d.Must, VisitorScope.Must);
 				Accept(v, d.MustNot, VisitorScope.MustNot);
 				Accept(v, d.Should, VisitorScope.Should);

src/Nest/QueryDsl/Visitor/VisitorScope.cs

@@ -4,6 +4,7 @@ public enum VisitorScope
 	{
 		Unknown,
 		Query,
+		Filter,
 		Must,
 		MustNot,
 		Should,
@@ -13,4 +14,4 @@ public enum VisitorScope
 		Span,
 
 	}
-}
+}