keep del when del-set-sequence exist in consumer-state

 Why I did it:
     when set after delete in a short time, consumer state may lost the del event.
     then what the multimap bring us for it may lost still.
 What I do:
     add the delete event even set after
     and modify the ut test for these changes.
     this can be verified by these testcase.

tests/redis_piped_state_ut.cpp

@@ -328,9 +328,16 @@ TEST(ConsumerStateTable, async_set_del_set)
         KeyOpFieldsValuesTuple kco;
         c.pop(kco);
         EXPECT_EQ(kfvKey(kco), key);
-        EXPECT_EQ(kfvOp(kco), "SET");
+        EXPECT_EQ(kfvOp(kco), "DEL");
 
         auto fvs = kfvFieldsValues(kco);
+        EXPECT_EQ(fvs.size(), 0U);
+
+        c.pop(kco);
+        EXPECT_EQ(kfvKey(kco), key);
+        EXPECT_EQ(kfvOp(kco), "SET");
+
+        fvs = kfvFieldsValues(kco);
         EXPECT_EQ(fvs.size(), (unsigned int)maxNumOfFields);
 
         map<string, string> mm;

tests/redis_state_ut.cpp

@@ -344,9 +344,16 @@ TEST(ConsumerStateTable, set_del_set)
         KeyOpFieldsValuesTuple kco;
         c.pop(kco);
         EXPECT_EQ(kfvKey(kco), key);
-        EXPECT_EQ(kfvOp(kco), "SET");
+        EXPECT_EQ(kfvOp(kco), "DEL");
 
         auto fvs = kfvFieldsValues(kco);
+        EXPECT_EQ(fvs.size(), 0U);
+
+        c.pop(kco);
+        EXPECT_EQ(kfvKey(kco), key);
+        EXPECT_EQ(kfvOp(kco), "SET");
+
+        fvs = kfvFieldsValues(kco);
         EXPECT_EQ(fvs.size(), (unsigned int)maxNumOfFields);
 
         map<string, string> mm;
@@ -451,9 +458,16 @@ TEST(ConsumerStateTable, set_pop_del_set_pop_get)
         KeyOpFieldsValuesTuple kco;
         c.pop(kco);
         EXPECT_EQ(kfvKey(kco), key);
-        EXPECT_EQ(kfvOp(kco), "SET");
+        EXPECT_EQ(kfvOp(kco), "DEL");
 
         auto fvs = kfvFieldsValues(kco);
+        EXPECT_EQ(fvs.size(), 0U);
+
+        c.pop(kco);
+        EXPECT_EQ(kfvKey(kco), key);
+        EXPECT_EQ(kfvOp(kco), "SET");
+
+        fvs = kfvFieldsValues(kco);
 
         /* size of fvs should be maxNumOfFields, no "field 1" left from first set*/
         EXPECT_EQ(fvs.size(), (unsigned int)maxNumOfFields);