Use size_t to calculate bytes needed for array.

src/array.c

@@ -20,15 +20,12 @@ static struct RArray*
 ary_new_capa(mrb_state *mrb, mrb_int capa)
 {
   struct RArray *a;
-  mrb_int blen;
+  size_t blen;
 
   if (capa > ARY_MAX_SIZE) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "array size too big");
   }
   blen = capa * sizeof(mrb_value);
-  if (blen < capa) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "array size too big");
-  }
 
   a = (struct RArray*)mrb_obj_alloc(mrb, MRB_TT_ARRAY, mrb->array_class);
   a->ptr = (mrb_value *)mrb_malloc(mrb, blen);