Call parseBody() in GetRelated before getting author

If the commit was previously parsed for headers only by RevWalk its
body can be missing, and the author is not available. Ensure subject
line and author is available when ChangeAndCommit builds the object.

Change-Id: If3179b9264ebbe86bcc1280a559d2e21f9803518

gerrit-server/src/main/java/com/google/gerrit/server/change/GetRelated.java

@@ -201,6 +201,7 @@ public class GetRelated implements RestReadView<RevisionResource> {
           c.add(seenCommit);
           q.addFirst(ps.getRevision().get());
           if (added.add(ps.getId().getParentKey())) {
+            rw.parseBody(c);
             graph.add(new ChangeAndCommit(change, ps, c));
           }
         }