[orca] Don't generate substring unnecessarily

[Joanmarie Diggs <joanied src gnome org>]

commit cd2f87dabcaa7706ab1465a371f3b79d66e84da3
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Mon Jan 9 10:03:05 2017 -0500

    Don't generate substring unnecessarily

 src/orca/generator.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/orca/generator.py b/src/orca/generator.py
index b2ecc16..a037f9c 100644
--- a/src/orca/generator.py
+++ b/src/orca/generator.py
@@ -903,7 +903,7 @@ class Generator:
         if start is None or end is None:
             return []
 
-        substring = self._script.utilities.substring(obj, start, end)
+        substring = args.get('string', self._script.utilities.substring(obj, start, end))
         if substring and not self._script.EMBEDDED_OBJECT_CHARACTER in substring:
             return [substring]