patch 9.1.0870: too many strlen() calls in eval.c

Problem:  too many strlen() calls in eval.c
Solution: Refactor eval.c to remove calls to STRLEN()
          (John Marriott)

closes: #16066

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 04967ef..12f7a88 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -11489,7 +11489,7 @@
 								|| flg == NULL)
 	rettv->vval.v_string = NULL;
     else
-	rettv->vval.v_string = do_string_sub(str, pat, sub, expr, flg);
+	rettv->vval.v_string = do_string_sub(str, STRLEN(str), pat, sub, expr, flg, NULL);
 }
 
 /*