Only offer "ignore thread" when there is a need for this

src/Object/Post.php

@@ -300,6 +300,7 @@ class Post
 		if ($this->isToplevel()) {
 			if(local_user()) {
 				$ignored = PostModel\ThreadUser::getIgnored($item['uri-id'], local_user());
+				if ($item['mention'] || $ignored) {
 					$ignore = [
 						'do'        => DI::l10n()->t("ignore thread"),
 						'undo'      => DI::l10n()->t("unignore thread"),
@@ -308,6 +309,7 @@ class Post
 						'classundo' => $ignored ? "" : "hidden",
 						'ignored'   => DI::l10n()->t('ignored'),
 					];
+				}
 
 				if ($conv->getProfileOwner() == local_user() && ($item['uid'] != 0)) {
 					if ($origin) {