Provide a quick fix to a crash in NVDA due to a bug shared between co…

…mtypes VARIANT implementation and ctypes callbacks. Re #3867

Stops crashes in NVDA's log viewer and in windbg, when either contains a large amount of text and then its some how updated.

source/_UIAHandler.py

@@ -1,6 +1,7 @@
 from ctypes import *
 from ctypes.wintypes import *
 import comtypes.client
+from comtypes.automation import VT_EMPTY
 from comtypes import *
 import weakref
 import threading
@@ -212,6 +213,9 @@ def IUIAutomationFocusChangedEventHandler_HandleFocusChangedEvent(self,sender):
 		eventHandler.queueEvent("gainFocus",obj)
 
 	def IUIAutomationPropertyChangedEventHandler_HandlePropertyChangedEvent(self,sender,propertyId,newValue):
+		# #3867: For now manually force this VARIANT type to empty to get around a nasty double free in comtypes/ctypes.
+		# We also don't use the value in this callback.
+		newValue.vt=VT_EMPTY
 		if not self.MTAThreadInitEvent.isSet():
 			# UIAHandler hasn't finished initialising yet, so just ignore this event.
 			return

user_docs/en/changes.t2t

@@ -60,6 +60,7 @@
  - Better reporting of JComboBox controls (html no longer reported, better reporting of expanded and collapsed states). (#3755)
  - More text is included in automatic dialog caption calculations. (#3757)
  - Changes to the name, value or description of the focused control is now reported more accurately. (#3770)
+- Fix a crash in NVDA seen in Windows 8 when focusing on certain RichEdit controls containing large amounts of text (e.g. NVDA's log viewer, windbg). (#3867)
 
 
 == Changes for Developers ==