Small stability improvement for HwndWrapper#WindowText(). This avoids exceptions of the form

Traceback (most recent call last):
	  File "pywinauto\controls\HwndWrapper.pyc", line 262, in WindowText
	  File "pywinauto\handleprops.pyc", line 58, in text
	  File "ctypes\__init__.pyc", line 310, in create_unicode_buffer
	ValueError: Array length must be >= 0, not -5880895

pywinauto/handleprops.py

@@ -52,7 +52,9 @@ def text(handle):
     length = length.value
 
     textval = ''
-    if length:
+    # In some rare cases, the length returned by WM_GETTEXTLENGTH is <0.
+    # Guard against this by checking it is >0 (==0 is not of interest):
+    if length > 0:
         length += 1
 
         buffer_ = ctypes.create_unicode_buffer(length)