scratch/igc/weak-undo-list 195d68f1013: * src/undo.c (scrub_undo_list): If possible, avoid mutation.

branch: scratch/igc/weak-undo-list
commit 195d68f10131e10751bdb876d1aca4ff83e641ce
Author: Helmut Eller <[email protected]>
Commit: Helmut Eller <[email protected]>

    * src/undo.c (scrub_undo_list): If possible, avoid mutation.
---
 src/undo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/undo.c b/src/undo.c
index a1af187567e..5487121fe40 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -193,7 +193,8 @@ scrub_undo_list (Lisp_Object list)
 	  Lisp_Object head = Fnthcdr (make_fixnum (4), entry);
 	  Lisp_Object pairs
 	    = scrub_id_offset_pairs (htab, XCDR (head));
-	  XSETCDR (head, pairs);
+	  if (pairs != XCDR (head))
+	    XSETCDR (head, pairs);
 	  drop = NILP (pairs);
 	}
       if (drop)