should use heap_eden->total_pages.

The size of page_list is heap_eden->total_pages, but
init_cursors() assumes the size of page_list is `heap_allocated_pages`.
This patch fix it.

gc.c

@@ -7496,15 +7496,16 @@ static void
 init_cursors(rb_objspace_t *objspace, struct heap_cursor *free, struct heap_cursor *scan, struct heap_page **page_list)
 {
     struct heap_page *page;
+    size_t total_pages = heap_eden->total_pages;
     page = page_list[0];
 
     free->index = 0;
     free->page = page;
     free->slot = page->start;
     free->objspace = objspace;
 
-    page = page_list[heap_allocated_pages - 1];
-    scan->index = heap_allocated_pages - 1;
+    page = page_list[total_pages - 1];
+    scan->index = total_pages - 1;
     scan->page = page;
     scan->slot = page->start + page->total_slots - 1;
     scan->objspace = objspace;