Fix the bug of creating an empty stitching rule when the label stack of the previous sub tunnel is full and there is no more labels to put.

Change-Id: I29318ec064e8c619ae900b1ecfb5b0390280d33d
diff --git a/src/main/java/net/onrc/onos/apps/segmentrouting/SegmentRoutingManager.java b/src/main/java/net/onrc/onos/apps/segmentrouting/SegmentRoutingManager.java
index 90af7cc..492dc33 100644
--- a/src/main/java/net/onrc/onos/apps/segmentrouting/SegmentRoutingManager.java
+++ b/src/main/java/net/onrc/onos/apps/segmentrouting/SegmentRoutingManager.java
@@ -1570,9 +1570,10 @@
         }
 
 
-        if (i < MAX_NUM_LABELS+1) {
+        if (i < MAX_NUM_LABELS+1 && (routeInfo.getFwdSwDpid() != null &&
+                !routeInfo.getFwdSwDpid().isEmpty())) {
             rules.add(routeInfo);
-            // NOTE: empty label stack can happen
+            // NOTE: empty label stack can happen, but forwarding destination should be set
         }
 
         return rules;