Simplify dummy root subject before comparing it to the current article

* lisp/gnus/gnus-sum.el (gnus-summary-prepare-threads): Simplify both
the dummy root and the following article before comparing them,
otherwise both the former and the latter might display the thread's
subject even when gnus-summary-line-format contains "%s" (bug#40520).

diff --git a/lisp/gnus/gnus-sum.el b/lisp/gnus/gnus-sum.el
index 341f04ad772bf1a11876aad97b3354e960d69ea0..1b0220a0f06a9a7458430619f41bcbade02a01b1 100644 (file)
--- a/lisp/gnus/gnus-sum.el
+++ b/lisp/gnus/gnus-sum.el
@@ -5352,7 +5352,8 @@ or a straight list of headers."
              ;; We remember that we probably want to output a dummy
              ;; root.
              (setq gnus-tmp-dummy-line gnus-tmp-header)
-             (setq gnus-tmp-prev-subject gnus-tmp-header))
+             (setq gnus-tmp-prev-subject
+                   (gnus-simplify-subject-fully gnus-tmp-header)))
             (t
              ;; We do not make a root for the gathered
              ;; sub-threads at all.