Fix socket availability issue in handle_tunnel_data

- Added check for valid target socket before attempting to send data
- Prevents 'Bad file descriptor' errors when local socket isn't ready yet
- Added debug message when target socket is not available
- Ensures tunnel_data messages are ignored until SSH connection is established
- Fixes race condition between WebSocket message arrival and SSH client connection

wssshtools/tunnel.c

@@ -412,7 +412,7 @@ void handle_tunnel_data(SSL *ssl __attribute__((unused)), const char *request_id
         return;
     }
 
-    int target_sock;
+    int target_sock = -1;
     if (active_tunnel->outgoing_buffer) {
         // wsscp: Use local_sock
         target_sock = active_tunnel->local_sock;
@@ -423,6 +423,16 @@ void handle_tunnel_data(SSL *ssl __attribute__((unused)), const char *request_id
         // wsssh: Use local_sock
         target_sock = active_tunnel->local_sock;
     }
+
+    // Check if target socket is valid
+    if (target_sock < 0) {
+        if (debug) {
+            printf("[DEBUG] Target socket not ready yet, ignoring tunnel_data\n");
+            fflush(stdout);
+        }
+        pthread_mutex_unlock(&tunnel_mutex);
+        return;
+    }
     pthread_mutex_unlock(&tunnel_mutex);
 
     // Validate hex data length