8345632: [ASAN] memory leak in get_numbered_property_as_sorted_string function

Reviewed-by: ccheung, dholmes

Author: SendaoYan

src/hotspot/share/classfile/modules.cpp

@@ -723,8 +723,7 @@ const char* Modules::get_numbered_property_as_sorted_string(const char* property
     }
   }
 
-  const char* result = (const char*)os::strdup(st.as_string()); // Example: "java.base,java.compiler"
-  return strcmp(result, "") != 0 ? result : nullptr;
+  return (st.size() > 0) ? os::strdup(st.as_string()) : nullptr;  // Example: "java.base,java.compiler"
 }
 
 void Modules::define_archived_modules(Handle h_platform_loader, Handle h_system_loader, TRAPS) {