Improve display of Labels/Projects/Assignees sort options (#25886)

Labels:
Before: (no highlights)

![image](https://github.com/go-gitea/gitea/assets/18380374/88ffbff0-1b14-4d93-810d-f2ce2b2d7321)
After:

![image](https://github.com/go-gitea/gitea/assets/18380374/ab7b665b-d17c-4acd-a681-64cbb67ae460)

![image](https://github.com/go-gitea/gitea/assets/18380374/19f8a0d0-ad5f-4dbf-b45a-1001e60a8399)

Projects:
Before: (no highlights)

![image](https://github.com/go-gitea/gitea/assets/18380374/2079e6a8-8801-4662-acda-e248f115462f)

After:

![image](https://github.com/go-gitea/gitea/assets/18380374/7180a086-68be-49c4-bb29-3d05454fb41d)

![image](https://github.com/go-gitea/gitea/assets/18380374/3c5a791f-1852-4957-89b8-10940c672e10)

Assignee:
Before: (no highlights)

![image](https://github.com/go-gitea/gitea/assets/18380374/09273636-d9b1-4144-9533-2ce66cab8c49)
After:

![image](https://github.com/go-gitea/gitea/assets/18380374/24bd0cfe-b589-4c8a-be67-74f242dda6d3)

![image](https://github.com/go-gitea/gitea/assets/18380374/7476be73-5201-4330-82e2-44b0b5080f71)

1 files changed, 5 insertions, 1 deletions

diff --git a/routers/web/repo/issue.go b/routers/web/repo/issue.go
index f5cec5a323..f243507c33 100644
--- a/routers/web/repo/issue.go
+++ b/routers/web/repo/issue.go
@@ -174,7 +174,11 @@ func issues(ctx *context.Context, milestoneID, projectID int64, isPullOption uti
 	// 0 means issues with no label
 	// blank means labels will not be filtered for issues
 	selectLabels := ctx.FormString("labels")
-	if len(selectLabels) > 0 {
+	if selectLabels == "" {
+		ctx.Data["AllLabels"] = true
+	} else if selectLabels == "0" {
+		ctx.Data["NoLabel"] = true
+	} else if len(selectLabels) > 0 {
 		labelIDs, err = base.StringsToInt64s(strings.Split(selectLabels, ","))
 		if err != nil {
 			ctx.ServerError("StringsToInt64s", err)