patch 8.2.0295: highlighting for :s wrong when using different separator

Problem:    Highlighting for :s wrong when using different separator.
Solution:   Use separat argument for search direction and separator. (Rob
            Pilling, closes #5665)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index b78e5ac..511e8c5 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3671,7 +3671,7 @@
 			curwin->w_cursor.col = 0;
 		    searchcmdlen = 0;
 		    flags = silent ? 0 : SEARCH_HIS | SEARCH_MSG;
-		    if (!do_search(NULL, c, cmd, 1L, flags, NULL))
+		    if (!do_search(NULL, c, c, cmd, 1L, flags, NULL))
 		    {
 			curwin->w_cursor = pos;
 			cmd = NULL;