[orca] Fix traceback

[Joanmarie Diggs <joanied src gnome org>]

commit 8847950c7ff127a882a5f344d8c1fb97fb672c42
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Wed Dec 28 11:03:43 2016 -0500

    Fix traceback

 src/orca/scripts/web/script_utilities.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/orca/scripts/web/script_utilities.py b/src/orca/scripts/web/script_utilities.py
index 68707a4..6743d9a 100644
--- a/src/orca/scripts/web/script_utilities.py
+++ b/src/orca/scripts/web/script_utilities.py
@@ -1292,7 +1292,7 @@ class Utilities(script_utilities.Utilities):
                 nextObj, nOffset = self.findNextCaretInOrder(nextObj, nOffset)
 
             onRight = self._getContentsForObj(nextObj, nOffset, boundary)
-            if self._contentIsSubsetOf(objects[0], onRight[-1]):
+            if onRight and self._contentIsSubsetOf(objects[0], onRight[-1]):
                 onRight = onRight[0:-1]
 
             onRight = list(filter(_include, onRight))