If rendering has failed due to a net.OpError stop rendering (#18642)

When a net.OpError occurs during rendering the underlying connection is essentially
dead and therefore attempting to render further data will only cause further errors.

Therefore in serverErrorInternal detect if the passed in error is an OpError and
if so do not attempt any further rendering.

Fix #18629

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/context/context.go

@@ -9,9 +9,11 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"html"
 	"html/template"
 	"io"
+	"net"
 	"net/http"
 	"net/url"
 	"path"
@@ -265,6 +267,12 @@ func (ctx *Context) ServerError(logMsg string, logErr error) {
 func (ctx *Context) serverErrorInternal(logMsg string, logErr error) {
 	if logErr != nil {
 		log.ErrorWithSkip(2, "%s: %v", logMsg, logErr)
+		if errors.Is(logErr, &net.OpError{}) {
+			// This is an error within the underlying connection
+			// and further rendering will not work so just return
+			return
+		}
+
 		if !setting.IsProd {
 			ctx.Data["ErrorMsg"] = logErr
 		}