[gnome-shell] runDialog: catch the case where no completion is available

[Cosimo Cecchi <cosimoc src gnome org>]

commit d54efe08382de35df765eb211386530a25f15e81
Author: Cosimo Cecchi <cosimo endlessm com>
Date:   Wed Aug 13 15:13:20 2014 -0700

    runDialog: catch the case where no completion is available
    
    Just return null, instead of failing with an exception later trying to
    call substr() on null.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=735062

 js/ui/runDialog.js |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/js/ui/runDialog.js b/js/ui/runDialog.js
index 1d5e7a5..9c9ee67 100644
--- a/js/ui/runDialog.js
+++ b/js/ui/runDialog.js
@@ -182,6 +182,10 @@ const RunDialog = new Lang.Class({
         let results = someResults.reduce(function(a, b) {
             return a.concat(b);
         }, []);
+
+        if (!results.length)
+            return null;
+
         let common = results.reduce(_getCommon, null);
         return common.substr(text.length);
     },