Properly restrict clarification thread to team.

Previously, the following could happen:
- team A requests a clarification, potentially including details the
  jury doesn't want to broadcast
- the jury replies to everyone, removing the part from the question that
  they don't want to have broadcasted
- team B views the reply from the jury, sees the whole clarification
  thread

Found while working on #3087

Author: meisterT

webapp/src/Controller/Team/ClarificationController.php

@@ -101,9 +101,12 @@ public function viewAction(Request $request, int $clarId): Response
             throw new HttpException(401, 'Permission denied');
         }
 
-        // Get the "parent" message if we have one.
+        // Get the "parent" message if we have one - if we have access to it
         if ($clarification->getInReplyTo()) {
-            $clarification = $clarification->getInReplyTo();
+            $parent = $clarification->getInReplyTo();
+            if ($team->canViewClarification($parent)) {
+                $clarification = $parent;
+            }
         }
 
         // Mark clarification as read.