fix(cruby): XML::Reader#attribute_hash returns nil on error

Note that on JRuby, the namespaces are still returned because the
parse error would raised on the subsequent node expansion.

This restores the behavior from v1.13.7

Author: flavorjones

CHANGELOG.md

@@ -4,6 +4,13 @@ Nokogiri follows [Semantic Versioning](https://semver.org/), please see the [REA
 
 ---
 
+## next / unreleased
+
+### Improvements
+
+* [CRuby] `XML::Reader#attribute_hash` now returns `nil` on parse errors. This restores the behavior of `#attributes` from v1.13.7 and earlier. [[#2715](https://github.com/sparklemotion/nokogiri/issues/2715)]
+
+
 ## 1.13.9 / 2022-10-18
 
 ### Security

ext/nokogiri/xml_reader.c

@@ -212,6 +212,10 @@ rb_xml_reader_attribute_hash(VALUE rb_reader)
   }
 
   c_node = xmlTextReaderExpand(c_reader);
+  if (c_node == NULL) {
+    return Qnil;
+  }
+
   c_property = c_node->properties;
   while (c_property != NULL) {
     VALUE rb_name = NOKOGIRI_STR_NEW2(c_property->name);

test/xml/test_reader.rb

@@ -681,6 +681,38 @@ def test_nonexistent_attribute
         reader.read # el
         assert_nil(reader.attribute("other"))
       end
+
+      def test_broken_markup_attribute_hash
+        xml = <<~XML
+          <root><foo bar="asdf" xmlns:quux="qwer">
+        XML
+        reader = Nokogiri::XML::Reader(xml)
+        reader.read # root
+        reader.read # foo
+
+        assert_equal("foo", reader.name)
+        if Nokogiri.jruby?
+          assert_equal({ "bar" => "asdf" }, reader.attribute_hash)
+        else
+          assert_nil(reader.attribute_hash)
+        end
+      end
+
+      def test_broken_markup_namespaces
+        xml = <<~XML
+          <root><foo bar="asdf" xmlns:quux="qwer">
+        XML
+        reader = Nokogiri::XML::Reader(xml)
+        reader.read # root
+        reader.read # foo
+
+        assert_equal("foo", reader.name)
+        if Nokogiri.jruby?
+          assert_equal({ "xmlns:quux" => "qwer" }, reader.namespaces)
+        else
+          assert_nil(reader.namespaces)
+        end
+      end
     end
   end
 end