Fix from review

Author: embhorn

src/tls.c

@@ -14994,7 +14994,9 @@ static int TLSX_GetSize(TLSX* list, byte* semaphore, byte msgType,
                 break;
         #ifdef WOLFSSL_CERT_WITH_EXTERN_PSK
             case TLSX_CERT_WITH_EXTERN_PSK:
-                ret = PSK_WITH_CERT_GET_SIZE(msgType, &length);
+                cbShim = 0;
+                ret = PSK_WITH_CERT_GET_SIZE(msgType, &cbShim);
+                length += cbShim;
                 break;
         #endif
         #endif