fix: add None check to CompiledPlugin.__del__ for extra safety

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: acoroleu-tempus

extism/extism.py

@@ -507,7 +507,7 @@ def __init__(
             raise Error(msg.decode())
 
     def __del__(self):
-        if not hasattr(self, "pointer") or self.pointer == -1:
+        if not hasattr(self, "pointer") or self.pointer is None or self.pointer == -1:
             return
         _lib.extism_compiled_plugin_free(self.pointer)
         self.pointer = -1