fix DTLS 1.2 cached ClientHello bug

Author: c-southwest

src/main/java/se/uu/it/dtlsfuzzer/components/sul/core/TlsSul.java

@@ -205,6 +205,10 @@ private void initializeTransportHandler() {
                         // try again
                     }
                 }
+                var firstClientHello = outputMapper.receiveOutput(context);
+                if (!firstClientHello.getName().equals("CLIENT_HELLO")) {
+                    LOGGER.fatal("The first Client Hello should have been received");
+                }
             }
         } catch (IOException e) {
             LOGGER.error("Could not initialize transport handler");