Fix EventHubs samples warnings (#4844)

Co-authored-by: Anton Kolesnyk <antkmsft@users.noreply.github.com>

sdk/eventhubs/azure-messaging-eventhubs/samples/basic-operations/create_consumer.cpp

@@ -26,6 +26,7 @@ int main()
   if (eventhubName == nullptr)
   {
     std::cerr << "Missing environment variable EVENTHUB_NAME" << std::endl;
+    return 1;
   }
 
   Azure::Messaging::EventHubs::ConsumerClient consumerClient(

sdk/eventhubs/azure-messaging-eventhubs/samples/basic-operations/create_producer.cpp

@@ -27,6 +27,7 @@ int main()
   if (eventhubName == nullptr)
   {
     std::cerr << "Missing environment variable EVENTHUB_NAME" << std::endl;
+    return 1;
   }
 
   Azure::Messaging::EventHubs::ProducerClient producerClient(

sdk/eventhubs/azure-messaging-eventhubs/samples/consume-events/consume_events.cpp

@@ -27,6 +27,7 @@ int main()
   if (eventhubName == nullptr)
   {
     std::cerr << "Missing environment variable EVENTHUB_NAME" << std::endl;
+    return 1;
   }
 
   /* Create a sample EventHubs application using a PartitionClient to read all the messages from an

sdk/eventhubs/azure-messaging-eventhubs/samples/produce-events/produce_events.cpp

@@ -27,6 +27,7 @@ int main()
   if (eventhubName == nullptr)
   {
     std::cerr << "Missing environment variable EVENTHUB_NAME" << std::endl;
+    return 1;
   }
 
   Azure::Messaging::EventHubs::ProducerClient producerClient(