[orca] Don't present listitem marker for a zero-length substring

[Joanmarie Diggs <joanied src gnome org>]

commit 588f23d2862b317904fc083b97ec461886d81a69
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Wed Jun 19 12:58:30 2019 -0400

    Don't present listitem marker for a zero-length substring

 src/orca/generator.py | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/orca/generator.py b/src/orca/generator.py
index a339113c8..c9d19283d 100644
--- a/src/orca/generator.py
+++ b/src/orca/generator.py
@@ -1006,6 +1006,10 @@ class Generator:
         if not (0 <= startOffset <= 1):
             return []
 
+        endOffset = args.get('endOffset')
+        if endOffset is not None and endOffset == startOffset:
+            return []
+
         listItemMarker = self._script.utilities.getListItemMarkerText(obj)
         if listItemMarker:
             return [listItemMarker]