Outdated comments in a non-checked out PR cause a console error (#3293)

Fixes #3289

Author: alexr00

src/view/pullRequestCommentController.ts

@@ -164,8 +164,9 @@ export class PullRequestCommentController implements CommentHandler, CommentReac
 				this._commentThreadCache[this.getCommentThreadCacheKey(fileName, isBase)] = threadsByPath[fileName]
 					.filter(
 						thread =>
-							(thread.diffSide === DiffSide.LEFT && isBase) ||
-							(thread.diffSide === DiffSide.RIGHT && !isBase),
+							((thread.diffSide === DiffSide.LEFT && isBase) ||
+							(thread.diffSide === DiffSide.RIGHT && !isBase))
+							&& (thread.line !== null),
 					)
 					.map(thread => {
 						const range = new vscode.Range(