Fix truncation of OpenSlide handle to 32 bits

Author: bgilbert

openslide/lowlevel.py

@@ -77,7 +77,7 @@ def from_param(cls, obj):
 def _check_open(result, _func, _args):
     if result is None:
         raise OpenSlideError("Could not open image file")
-    return _OpenSlide(result)
+    return _OpenSlide(c_void_p(result))
 
 # prevent further operations on slide handle after it is closed
 def _check_close(_result, _func, args):