Fix project filter bugs (#26490)

related: #26012

### Bugs
1. missing project filter on the issue page.

1e76a824bc/modules/indexer/issues/dboptions.go (L11-L15)
3. incorrect SQL condition: some issue does not belong to a project but
exists on the project_issue table.

f5dbac9d36/models/issues/issue_search.go (L233)

### Before:

![before](https://github.com/go-gitea/gitea/assets/50507092/1dcde39e-3e2f-4151-b2c6-4d67bf493c2f)

### After:

![after](https://github.com/go-gitea/gitea/assets/50507092/badfb81f-056d-4a2f-9838-1cba9c15768d)

---------

Co-authored-by: Giteabot <teabot@gitea.io>

modules/indexer/issues/dboptions.go

@@ -17,6 +17,10 @@ func ToSearchOptions(keyword string, opts *issues_model.IssuesOptions) *SearchOp
 		IsClosed:  opts.IsClosed,
 	}
 
+	if opts.ProjectID != 0 {
+		searchOpt.ProjectID = &opts.ProjectID
+	}
+
 	if len(opts.LabelIDs) == 1 && opts.LabelIDs[0] == 0 {
 		searchOpt.NoLabelOnly = true
 	} else {