refactor: Use getattr for robust attribute access within the release method.

Author: bhatt4982

spannerlib/wrappers/spannerlib-python/spannerlib-python/google/cloud/spannerlib/internal/message.py

@@ -125,7 +125,7 @@ def raise_if_error(self) -> None:
 
     def release(self) -> None:
         """Releases memory using the injected library instance."""
-        if self._is_released:
+        if getattr(self, "_is_released", False):
             return
 
         self._is_released = True
@@ -135,7 +135,8 @@ def release(self) -> None:
             return
 
         # 2. Check if we have the tool to free it
-        if self._lib is None:
+        lib = getattr(self, "_lib", None)
+        if lib is None:
             logger.critical(
                 "Message (pinner=%d) cannot be released! "
                 "Library dependency was not injected via bind_library().",