some improvement to Libxml2Document cleanup: avoid noisy errors, and make sure both cleaning up functions are called

scrapy/xpath/document.py

@@ -12,11 +12,19 @@ class Libxml2Document(object):
         self.xpathContext = self.xmlDoc.xpathNewContext()
 
     def __del__(self):
-        if hasattr(self, 'xmlDoc'):
+        # we must call both cleanup functions, so we try/except all exceptions
+        # to make sure one doesn't prevent the other from being called
+        # this call sometimes raises a "NoneType is not callable" TypeError
+        # also, these calls sometimes raise a "NoneType is not callable"
+        # TypeError, so the try/except block silences them
+        try:
             self.xmlDoc.freeDoc()
-        if hasattr(self, 'xpathContext'):
+        except:
+            pass
+        try:
             self.xpathContext.xpathFreeContext()
+        except:
+            pass
 
     def __str__(self):
         return "<Libxml2Document %s>" % self.xmlDoc.name
-