[orca/gnome-3-22] Don't assume we can always get a string value for Calc input line

[Joanmarie Diggs <joanied src gnome org>]

commit 0e8a9021032ebde6b583896155015361c3d5e05c
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Mon Dec 5 05:42:37 2016 -0500

    Don't assume we can always get a string value for Calc input line

 src/orca/scripts/apps/soffice/speech_generator.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/orca/scripts/apps/soffice/speech_generator.py 
b/src/orca/scripts/apps/soffice/speech_generator.py
index 88e6231..cdfb277 100644
--- a/src/orca/scripts/apps/soffice/speech_generator.py
+++ b/src/orca/scripts/apps/soffice/speech_generator.py
@@ -343,7 +343,7 @@ class SpeechGenerator(speech_generator.SpeechGenerator):
             return []
 
         text = self._script.utilities.displayedText(inputLine)
-        if text.startswith("="):
+        if text and text.startswith("="):
             result = [messages.HAS_FORMULA]
             result.extend(self.voice(speech_generator.SYSTEM))
             return result