fix(css-selector): default XML namespace is not applied to wildcard

When performing a CSS selector query, an XML document's root namespace
declarations are injected into the XPathVisitor, and the default
namespace is applied to any non-namespaced element in the resulting
xpath query.

However, the wildcard selector "*" should not have this namespace
applied. This regressed in v1.17.0 with 179d74d.

Fixes #3411

lib/nokogiri/css/xpath_visitor.rb

@@ -283,7 +283,8 @@ def visit_element_name(node)
           else
             node.value.join(":")
           end
-        elsif @namespaces&.key?("xmlns") # apply the default namespace if it's declared
+        elsif node.value.first != "*" && @namespaces&.key?("xmlns")
+          # apply the default namespace (if one is present) to a non-wildcard selector
           "xmlns:#{node.value.first}"
         else
           node.value.first

test/css/test_xpath_visitor.rb

@@ -164,6 +164,13 @@ def visit_pseudo_class_aaron(node)
         )
       end
 
+      it "default namespace is not applied to wildcard selectors" do
+        assert_equal(
+          ["//xmlns:a//*"],
+          Nokogiri::CSS.xpath_for("a *", ns: ns, cache: false),
+        )
+      end
+
       it "intentionally-empty namespace omits the default xmlns" do
         # An intentionally-empty namespace
         assert_equal(["//a"], Nokogiri::CSS.xpath_for("|a", ns: ns, cache: false))