threshold: fix handling of multiple threshold.

This patch fixes the unittest and may fix the real work.

src/detect-engine-alert.c

@@ -74,16 +74,18 @@ static int PacketAlertHandle(DetectEngineCtx *de_ctx, DetectEngineThreadCtx *det
         SCReturnInt(1);
     }
 
-    while ((td = SigGetThresholdTypeIter(s, p, &sm))) {
+    do {
+        td = SigGetThresholdTypeIter(s, p, &sm);
+        if (td != NULL) {
             SCLogDebug("td %p", td);
             ret = PacketAlertThreshold(de_ctx, det_ctx, td, p, s);
             if (ret == 0) {
                 /* It doesn't match threshold, remove it */
                 PacketAlertRemove(p, pos);
-            /* no need to iterate */
                 break;
             }
         }
+    } while (sm != NULL);
 
     SCReturnInt(ret);
 }