[Bug #1196] Assign task to the first valid queue in case that all of them are empty.

Until now, the task wasn't assigned to any queue when they were all empty,
causing this bug.

FEA: ItEr75S04BugFixing

navalplanner-webapp/src/main/java/org/navalplanner/web/limitingresources/LimitingResourceQueueModel.java

@@ -729,6 +729,9 @@ public class LimitingResourceQueueModel implements ILimitingResourceQueueModel {
                 }
             }
         }
+        if(result == null && !potentiallyValidQueues.isEmpty()) {
+            result = potentiallyValidQueues.get(0);
+        }
         return result;
     }