Check mjs_getName return value in XML parser. Fixes #2898.

PiperOrigin-RevId: 819351410
Change-Id: I0807d71328068f6388991ae15274c7d61b4d3e53

test/xml/xml_native_reader_test.cc

@@ -1529,7 +1529,7 @@ TEST_F(XMLReaderTest, ParseReplicateRepeatedName) {
   mjSpec* spec = mj_parseXMLString(xml, 0, error.data(), error.size());
   EXPECT_THAT(spec, IsNull()) << error.data();
   EXPECT_THAT(error.data(), HasSubstr("repeated name 'b' in actuator"));
-  EXPECT_THAT(error.data(), HasSubstr("Element 'replicate'"));
+  EXPECT_THAT(error.data(), HasSubstr("Element 'position'"));
 }
 
 TEST_F(XMLReaderTest, RepeatedPrefix) {

test/xml/xml_native_writer_test.cc

@@ -1417,6 +1417,8 @@ TEST_F(XMLWriterTest, WriteReadCompare) {
         auto abs_path = p.path();
         mjSpec* stemp = mj_parseXMLString(SaveAndReadXml(s).c_str(), 0,
                                           error.data(), error.size());
+        ASSERT_THAT(stemp, NotNull())
+            << "Failed to load " << xml.c_str() << ": " << error.data();
         mjs_setString(stemp->modelfiledir,
                       abs_path.remove_filename().string().c_str());
         mjModel* mtemp = mj_compile(stemp, nullptr);