Show pull request selection even when unrelated branches (#11239)

Fix #10525

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

routers/repo/compare.go

@@ -320,9 +320,6 @@ func PrepareCompareDiff(
 	compareInfo.Commits = models.ParseCommitsWithStatus(compareInfo.Commits, headRepo)
 	ctx.Data["Commits"] = compareInfo.Commits
 	ctx.Data["CommitCount"] = compareInfo.Commits.Len()
-	if ctx.Data["CommitCount"] == 0 {
-		ctx.Data["PageIsComparePull"] = false
-	}
 
 	if compareInfo.Commits.Len() == 1 {
 		c := compareInfo.Commits.Front().Value.(models.SignCommitWithStatuses)

templates/repo/diff/compare.tmpl

@@ -59,7 +59,7 @@
 
 	{{if .IsNothingToCompare}}
     	<div class="ui segment">{{.i18n.Tr "repo.pulls.nothing_to_compare"}}</div>
-	{{else if .PageIsComparePull}}
+	{{else if and .PageIsComparePull (gt .CommitCount 0)}}
 		{{if .HasPullRequest}}
         	<div class="ui segment">
         		{{.i18n.Tr "repo.pulls.has_pull_request" $.RepoLink $.RepoRelPath .PullRequest.Index | Safe}}