Do not close the connection abruptly on too big file uploads (#9083)

api4/brand.go

@@ -4,6 +4,8 @@
 package api4
 
 import (
+	"io"
+	"io/ioutil"
 	"net/http"
 
 	"github.com/mattermost/mattermost-server/model"
@@ -27,6 +29,8 @@ func getBrandImage(c *Context, w http.ResponseWriter, r *http.Request) {
 }
 
 func uploadBrandImage(c *Context, w http.ResponseWriter, r *http.Request) {
+	defer io.Copy(ioutil.Discard, r.Body)
+
 	if r.ContentLength > *c.App.Config().FileSettings.MaxFileSize {
 		c.Err = model.NewAppError("uploadBrandImage", "api.admin.upload_brand_image.too_large.app_error", nil, "", http.StatusRequestEntityTooLarge)
 		return