Prevent adding nil label to .AddedLabels or .RemovedLabels

There are possibly a few old databases out there with malmigrated data that can
cause panics with empty labels being migrated.

This PR adds a few tests to prevent nil labels being added.

Fix go-gitea#14466

Signed-off-by: Andrew Thornton <[email protected]>

Author: zeripath

modules/templates/helper.go

@@ -371,6 +371,10 @@ func NewFuncMap() []template.FuncMap {
 		"RenderLabels": func(labels []*models.Label) template.HTML {
 			html := `<span class="labels-list">`
 			for _, label := range labels {
+				// Protect against nil value in labels - shouldn't happen but would cause a panic if so
+				if label == nil {
+					continue
+				}
 				html += fmt.Sprintf("<div class='ui label' style='color: %s; background-color: %s'>%s</div> ",
 					label.ForegroundColor(), label.Color, RenderEmoji(label.Name))
 			}

routers/repo/issue.go

@@ -2464,7 +2464,7 @@ func combineLabelComments(issue *models.Issue) {
 		if i == 0 || cur.Type != models.CommentTypeLabel ||
 			(prev != nil && prev.PosterID != cur.PosterID) ||
 			(prev != nil && cur.CreatedUnix-prev.CreatedUnix >= 60) {
-			if cur.Type == models.CommentTypeLabel {
+			if cur.Type == models.CommentTypeLabel && cur.Label != nil {
 				if cur.Content != "1" {
 					cur.RemovedLabels = append(cur.RemovedLabels, cur.Label)
 				} else {
@@ -2474,10 +2474,12 @@ func combineLabelComments(issue *models.Issue) {
 			continue
 		}
 
-		if cur.Content != "1" {
-			prev.RemovedLabels = append(prev.RemovedLabels, cur.Label)
-		} else {
-			prev.AddedLabels = append(prev.AddedLabels, cur.Label)
+		if cur.Label != nil {
+			if cur.Content != "1" {
+				prev.RemovedLabels = append(prev.RemovedLabels, cur.Label)
+			} else {
+				prev.AddedLabels = append(prev.AddedLabels, cur.Label)
+			}
 		}
 		prev.CreatedUnix = cur.CreatedUnix
 		issue.Comments = append(issue.Comments[:i], issue.Comments[i+1:]...)