fix: distribute panic

middleware/distributor.go

 package middleware
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"one-api/common"
@@ -25,6 +26,10 @@ func Distribute() func(c *gin.Context) {
 		var channel *model.Channel
 		channelId, ok := c.Get("specific_channel_id")
 		modelRequest, shouldSelectChannel, err := getModelRequest(c)
+		if err != nil {
+			abortWithOpenAiMessage(c, http.StatusBadRequest, "Invalid request, "+err.Error())
+			return
+		}
 		userGroup, _ := model.CacheGetUserGroup(userId)
 		c.Set("group", userGroup)
 		if ok {
@@ -141,7 +146,7 @@ func getModelRequest(c *gin.Context) (*ModelRequest, bool, error) {
 	}
 	if err != nil {
 		abortWithOpenAiMessage(c, http.StatusBadRequest, "无效的请求, "+err.Error())
-		return nil, false, err
+		return nil, false, errors.New("无效的请求, " + err.Error())
 	}
 	if strings.HasPrefix(c.Request.URL.Path, "/v1/moderations") {
 		if modelRequest.Model == "" {