[orca] Add a null check

[Joanmarie Diggs <joanied src gnome org>]

commit 7c3f409bb33bb0d4fb4340f0f2cebb85871058a7
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Fri Jun 7 18:14:37 2019 -0400

    Add a null check

 src/orca/scripts/web/script_utilities.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/orca/scripts/web/script_utilities.py b/src/orca/scripts/web/script_utilities.py
index a9b0923b7..77e46775e 100644
--- a/src/orca/scripts/web/script_utilities.py
+++ b/src/orca/scripts/web/script_utilities.py
@@ -407,7 +407,8 @@ class Utilities(script_utilities.Utilities):
         if self._script.useFocusMode(obj) != self._script.inFocusMode():
             self._script.togglePresentationMode(None)
 
-        obj.clearCache()
+        if obj:
+            obj.clearCache()
 
         # TODO - JD: This is private.
         self._script._saveFocusedObjectInfo(obj)