BF: Disable the Form aperture on creation, enable only on draw

This fix stops the aperture from being drawn when the Form is created.
This was causing the aperture to persist over all routines, until the
Form was actually drawn, where the aperture could be disabled.

Author: dvbridges

psychopy/visual/form.py

@@ -596,13 +596,15 @@ def _setAperture(self):
         psychopy.visual.Aperture
             The aperture setting viewable area for forms
         """
-        return psychopy.visual.Aperture(win=self.win,
-                                        name='aperture',
-                                        units=self.units,
-                                        shape='square',
-                                        size=self.size,
-                                        pos=(0, 0),
-                                        autoLog=False)
+        aperture = psychopy.visual.Aperture(win=self.win,
+                                            name='aperture',
+                                            units=self.units,
+                                            shape='square',
+                                            size=self.size,
+                                            pos=(0, 0),
+                                            autoLog=False)
+        aperture.disable()  # Disable on creation. Only enable on draw.
+        return aperture
 
     def _getScrollOffset(self):
         """Calculate offset position of items in relation to markerPos