Reduced the number of preprocessor directives.
diff --git a/src/core/ngx_slab.c b/src/core/ngx_slab.c
index 3d56603..782792d 100644
--- a/src/core/ngx_slab.c
+++ b/src/core/ngx_slab.c
@@ -45,9 +45,7 @@
 
 #define ngx_slab_junk(p, size)     ngx_memset(p, 0xA5, size)
 
-#else
-
-#if (NGX_HAVE_DEBUG_MALLOC)
+#elif (NGX_HAVE_DEBUG_MALLOC)
 
 #define ngx_slab_junk(p, size)                                                \
     if (ngx_debug_malloc)          ngx_memset(p, 0xA5, size)
@@ -58,8 +56,6 @@
 
 #endif
 
-#endif
-
 static ngx_slab_page_t *ngx_slab_alloc_pages(ngx_slab_pool_t *pool,
     ngx_uint_t pages);
 static void ngx_slab_free_pages(ngx_slab_pool_t *pool, ngx_slab_page_t *page,