fix

Author: wxiaoguang

templates/repo/diff/section_unified.tmpl

@@ -1,5 +1,7 @@
 {{$file := .file}}
-{{$blobExcerptLink := print (or ctx.RootData.CommitRepoLink ctx.RootData.RepoLink) (Iif $.root.PageIsWiki "/wiki" "") "/blob_excerpt/" (PathEscape $.root.AfterCommitID) "?"}}
+{{$repoLink := or ctx.RootData.CommitRepoLink ctx.RootData.RepoLink}}
+{{$afterCommitID := or $.root.AfterCommitID "no-after-commit-id"}}{{/* this tmpl is also used by the PR Conversation page, so the "AfterCommitID" may not exist */}}
+{{$blobExcerptLink := print $repoLink (Iif $.root.PageIsWiki "/wiki" "") "/blob_excerpt/" (PathEscape $afterCommitID) "?"}}
 <colgroup>
 	<col width="50">
 	<col width="50">