Swarming UI: Fix issue with negative pending time.

appengine/swarming/ui/build/elements.html

Index: appengine/swarming/ui/build/elements.html
diff --git a/appengine/swarming/ui/build/elements.html b/appengine/swarming/ui/build/elements.html
index 85b042a05c4cf383b8384f8897da5dd558bacbff..c1536b056f9c84371bb67d915b38d3a05f2ff759 100644
--- a/appengine/swarming/ui/build/elements.html
+++ b/appengine/swarming/ui/build/elements.html
@@ -1299,7 +1299,11 @@ monthsShort:"innayr_brˤayrˤ_marˤsˤ_ibrir_mayyw_ywnyw_ywlywz_ɣwšt_šwtanbir
       },
 
       _duration: function(start, end) {
-        return end.getTime() - start.getTime();
+        var duration = end.getTime() - start.getTime();
+        if (duration < 0) {
+          duration = 0;
+        }
+        return duration;
       },
 
       _empty: function(array) {