[orca] Add sanity check for line contents before attempting to present them

[Joanmarie Diggs <joanied src gnome org>]

commit d6c6ca9f2892f912036ace54e8ce85c0ffe6035f
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Fri Jun 26 19:01:03 2015 -0400

    Add sanity check for line contents before attempting to present them

 src/orca/caret_navigation.py |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/src/orca/caret_navigation.py b/src/orca/caret_navigation.py
index ebd17f0..4c7ef13 100644
--- a/src/orca/caret_navigation.py
+++ b/src/orca/caret_navigation.py
@@ -323,6 +323,9 @@ class CaretNavigation:
                 return True
 
         contents = script.utilities.getNextLineContents()
+        if not contents:
+            return False
+
         obj, start = contents[0][0], contents[0][1]
         script.utilities.setCaretPosition(obj, start)
         script.speakContents(contents)
@@ -345,6 +348,9 @@ class CaretNavigation:
 
 
         contents = script.utilities.getPreviousLineContents()
+        if not contents:
+            return False
+
         obj, start = contents[0][0], contents[0][1]
         script.utilities.setCaretPosition(obj, start)
         script.speakContents(contents)