[orca] Add sanity check to isLink() to be sure we have an object

[Joanmarie Diggs <joanied src gnome org>]

commit a0d3921a59bb415ac1111c526b3dfaf2f8a251ab
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Wed Jun 3 18:43:43 2015 -0400

    Add sanity check to isLink() to be sure we have an object

 .../scripts/toolkits/Gecko/script_utilities.py     |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/orca/scripts/toolkits/Gecko/script_utilities.py 
b/src/orca/scripts/toolkits/Gecko/script_utilities.py
index a8b8f49..9a1af40 100644
--- a/src/orca/scripts/toolkits/Gecko/script_utilities.py
+++ b/src/orca/scripts/toolkits/Gecko/script_utilities.py
@@ -1492,6 +1492,9 @@ class Utilities(script_utilities.Utilities):
         return rv
 
     def isLink(self, obj):
+        if not obj:
+            return False
+
         rv = self._isLink.get(hash(obj))
         if rv is not None:
             return rv