fix slab page or more sized allocations if nginx was build without debug
diff --git a/src/core/ngx_slab.c b/src/core/ngx_slab.c
index b187026..a74dcd9 100644
--- a/src/core/ngx_slab.c
+++ b/src/core/ngx_slab.c
@@ -661,11 +661,8 @@
             }
 
             page->slab = pages | NGX_SLAB_PAGE_START;
-
-#if (NGX_DEBUG)
             page->next = NULL;
             page->prev = NGX_SLAB_PAGE;
-#endif
 
             if (--pages == 0) {
                 return page;
@@ -673,10 +670,8 @@
 
             for (p = page + 1; pages; pages--) {
                 p->slab = NGX_SLAB_PAGE_BUSY;
-#if (NGX_DEBUG)
                 p->next = NULL;
                 p->prev = NGX_SLAB_PAGE;
-#endif
                 p++;
             }