Clean cached messages on destroy kafka consumer

The callchain of the kafka consumer is very tricky, so for the sake of
common sense let's just clean the messages on moving out consumer (and
in dtor, but this is just to keep that two code path in sync).

(Also reported by @filimonov)

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>

src/Storages/Kafka/KafkaConsumer.cpp

@@ -153,6 +153,7 @@ void KafkaConsumer::createConsumer(cppkafka::Configuration consumer_config)
 
 ConsumerPtr && KafkaConsumer::moveConsumer()
 {
+    cleanUnprocessed();
     if (!consumer->get_subscription().empty())
     {
         try
@@ -173,6 +174,7 @@ KafkaConsumer::~KafkaConsumer()
     if (!consumer)
         return;
 
+    cleanUnprocessed();
     try
     {
         if (!consumer->get_subscription().empty())