patch 8.2.4255: theoretical computation overflow

Problem:    Theoretical computation overflow.
Solution:   Perform multiplication in a wider type. (closes #9657)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 879fe22..cb5fcfe 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -7327,7 +7327,7 @@
 		if ((l->lv_u.nonmat.lv_stride > 0) ^ domax)
 		    n = l->lv_u.nonmat.lv_start;
 		else
-		    n = l->lv_u.nonmat.lv_start + (l->lv_len - 1)
+		    n = l->lv_u.nonmat.lv_start + ((varnumber_T)l->lv_len - 1)
 						    * l->lv_u.nonmat.lv_stride;
 	    }
 	    else