patch 8.2.4255: theoretical computation overflow

Problem:    Theoretical computation overflow.
Solution:   Perform multiplication in a wider type. (closes #9657)
diff --git a/src/list.c b/src/list.c
index f4fddbd..ff7d5ab 100644
--- a/src/list.c
+++ b/src/list.c
@@ -2902,7 +2902,7 @@
 	if (l->lv_first == &range_list_item)
 	{
 	    varnumber_T new_start = l->lv_u.nonmat.lv_start
-		+ (l->lv_len - 1) * l->lv_u.nonmat.lv_stride;
+		+ ((varnumber_T)l->lv_len - 1) * l->lv_u.nonmat.lv_stride;
 	    l->lv_u.nonmat.lv_end = new_start
 		- (l->lv_u.nonmat.lv_end - l->lv_u.nonmat.lv_start);
 	    l->lv_u.nonmat.lv_start = new_start;