Disallow empty titles (#5785)

* add util method and tests

* make sure the title of an issue cannot be empty

* wiki title cannot be empty

* pull request title cannot be empty

* update to make use of the new util methof

routers/repo/pull.go

@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/notification"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
 
 	"github.com/Unknwon/com"
 )
@@ -875,6 +876,16 @@ func CompareAndPullRequestPost(ctx *context.Context, form auth.CreateIssueForm)
 		return
 	}
 
+	if util.IsEmptyString(form.Title) {
+		PrepareCompareDiff(ctx, headUser, headRepo, headGitRepo, prInfo, baseBranch, headBranch)
+		if ctx.Written() {
+			return
+		}
+
+		ctx.RenderWithErr(ctx.Tr("repo.issues.new.title_empty"), tplComparePull, form)
+		return
+	}
+
 	patch, err := headGitRepo.GetPatch(prInfo.MergeBase, headBranch)
 	if err != nil {
 		ctx.ServerError("GetPatch", err)