Fix Pr Create crash (#823)

Fix #822

Reviewed-on: https://gitea.com/gitea/tea/pulls/823
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-committed-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/interact/pull_create.go

@@ -33,7 +33,7 @@ func CreatePull(ctx *context.TeaContext) (err error) {
 	if ctx.LocalRepo != nil {
 		headOwner, headBranch, err = task.GetDefaultPRHead(ctx.LocalRepo)
 		if err == nil {
-			validator = nil
+			validator = func(string) error { return nil }
 		}
 	}