patch 9.1.1262: heap-buffer-overflow with narrow 'pummaxwidth' value

Problem:  heap-buffer-overflow occurs with narrow 'pummaxwidth' value
          (after v9.1.1250)
Solution: test that st_end points after st pointer (Hirohito Higashi)

closes: #17005

Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/popupmenu.c b/src/popupmenu.c
index 71bb499..a7c20c1 100644
--- a/src/popupmenu.c
+++ b/src/popupmenu.c
@@ -845,7 +845,7 @@
 				    last_char = st_end;
 				}
 
-				if (last_char != NULL)
+				if (last_char != NULL && st_end > st)
 				{
 				    if (used_cells < ellipsis_width)
 				    {