xpath: fix a bug that no namespace attribute isn't matched with prefix

[ruby-list:50733]

Reported by Yasuhiro KIMURA. Thanks!!!

Author: kou

lib/rexml/xpath_parser.rb

@@ -499,7 +499,11 @@ def node_test(path_stack, nodesets, any_type: :element)
               else
                 # FIXME: This DOUBLES the time XPath searches take
                 ns = get_namespace(raw_node.element, prefix)
-                raw_node.name == name and raw_node.namespace == ns
+                if ns.empty?
+                  raw_node.name == name and raw_node.prefix.empty?
+                else
+                  raw_node.name == name and raw_node.namespace == ns
+                end
               end
             else
               false

test/rexml/xpath/test_attribute.rb

@@ -7,7 +7,7 @@ class TestXPathAttribute < Test::Unit::TestCase
     def setup
       @xml = <<-XML
 <?xml version="1.0" encoding="UTF-8"?>
-<root>
+<root xmlns="http://example.com/">
   <child name="one">child1</child>
   <child name="two">child2</child>
   <child name="three">child3</child>
@@ -26,5 +26,13 @@ def test_xpath_each
       children = REXML::XPath.each(@document, "/root/child[@name='two']")
       assert_equal(["child2"], children.collect(&:text))
     end
+
+    def test_no_namespace
+      children = REXML::XPath.match(@document,
+                                    "/root/child[@nothing:name='two']",
+                                    "" => "http://example.com/",
+                                    "nothing" => "")
+      assert_equal(["child2"], children.collect(&:text))
+    end
   end
 end