Fix drwetter#2599

This commit fixes drwetter#2599 by not wrapping fileout() messages in a "clientProblem" wrapper if TLS13_ONLY is set. The TLS13_ONLY flag being set is an indicator that fileout_banner() has already been called.

testssl.sh

@@ -1371,13 +1371,17 @@ fileout_insert_warning() {
      [[ "$CMDLINE=" =~ -iL ]] && return 0
      # Note we still have the message on screen + in HTML which is not as optimal as it could be
 
-     if "$do_pretty_json" && "$JSONHEADER"; then
+     # See #2599. The "clientProblem" wrapper should only be added if fileout_insert_warning()
+     # is called before fileout_banner(). The only instance in which this function is called
+     # after fileout_banner() is in the case of a TLS 1.3 only server when $OPENSSL does not
+     # support TLS 1.3.
+     if "$do_pretty_json" && "$JSONHEADER" && ! "$TLS13_ONLY"; then
           echo -e "          \"clientProblem${CLIENT_PROB_NO}\" : [" >>"$JSONFILE"
           CLIENT_PROB_NO=$((CLIENT_PROB_NO + 1))
           FIRST_FINDING=true       # make sure we don't have a comma here
      fi
      fileout "$1" "$2" "$3"
-     if "$do_pretty_json"; then
+     if "$do_pretty_json" && ! "$TLS13_ONLY"; then
           if "$JSONHEADER"; then
                echo -e "\n          ]," >>"$JSONFILE"
           else