fix: check cert files exist

main.go

@@ -2,9 +2,11 @@ package webtransport
 
 import (
 	"net/http"
+	"os"
 	"strconv"
 
 	"github.com/quic-go/quic-go"
+	"go.uber.org/zap"
 	. "m7s.live/engine/v4"
 )
 
@@ -17,6 +19,18 @@ type WebTransportConfig struct {
 func (c *WebTransportConfig) OnEvent(event any) {
 	switch event.(type) {
 	case FirstConfig:
+		_, err := os.Stat(c.CertFile)
+		if err != nil {
+			plugin.Error("need certfile", zap.Error(err))
+			plugin.Disabled = true
+			return
+		}
+		_, err = os.Stat(c.KeyFile)
+		if err != nil {
+			plugin.Error("need keyfile", zap.Error(err))
+			plugin.Disabled = true
+			return
+		}
 		mux := http.NewServeMux()
 		mux.HandleFunc("/play/", func(w http.ResponseWriter, r *http.Request) {
 			streamPath := r.URL.Path[len("/play/"):]