fix diff method can not be added to RadixTree

Author: Stellar1999

dubbo-rpc/dubbo-rpc-triple/src/main/java/org/apache/dubbo/rpc/protocol/tri/rest/mapping/RadixTree.java

@@ -83,9 +83,12 @@ public T addPath(PathExpression path, T value) {
             Node<T> child = getChild(current, segments[i]);
             if (i == len - 1) {
                 List<Pair<PathExpression, T>> values = child.values;
-                for (int j = 0, size = values.size(); j < size; j++) {
-                    if (values.get(j).getLeft().equals(path)) {
-                        return values.get(j).getRight();
+                for (Pair<PathExpression, T> pathExpressionTPair : values) {
+                    if (pathExpressionTPair.getLeft().equals(path)) {
+                        T rightVal = pathExpressionTPair.getRight();
+                        if (rightVal.equals(value)) {
+                            return rightVal;
+                        }
                     }
                 }
                 values.add(Pair.of(path, value));