Fix bug filtering issues which have no project (go-gitea#31337)

Fix go-gitea#31327
This is a quick patch to fix the bug.
Some parameters are using 0, some are using -1. I think it needs a
refactor to keep consistent. But that will be another PR.

modules/indexer/issues/dboptions.go

@@ -38,6 +38,12 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		searchOpt.MilestoneIDs = opts.MilestoneIDs
 	}
 
+	if opts.ProjectID > 0 {
+		searchOpt.ProjectID = optional.Some(opts.ProjectID)
+	} else if opts.ProjectID == -1 { // FIXME: this is inconsistent from other places
+		searchOpt.ProjectID = optional.Some[int64](0) // Those issues with no project(projectid==0)
+	}
+
 	// See the comment of issues_model.SearchOptions for the reason why we need to convert
 	convertID := func(id int64) optional.Option[int64] {
 		if id > 0 {
@@ -49,7 +55,6 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		return nil
 	}
 
-	searchOpt.ProjectID = convertID(opts.ProjectID)
 	searchOpt.ProjectBoardID = convertID(opts.ProjectBoardID)
 	searchOpt.PosterID = convertID(opts.PosterID)
 	searchOpt.AssigneeID = convertID(opts.AssigneeID)