Cache: fixed slots accounting error introduced in c9d680b00744.

src/http/ngx_http_file_cache.c

diff --git a/src/http/ngx_http_file_cache.c b/src/http/ngx_http_file_cache.c
index 63ce6bb..3561028 100644
--- a/src/http/ngx_http_file_cache.c
+++ b/src/http/ngx_http_file_cache.c
@@ -2115,12 +2115,12 @@
                            "could not allocate node%s", cache->shpool->log_ctx);
             }
 
-            cache->sh->count++;
-
             ngx_shmtx_unlock(&cache->shpool->mutex);
             return NGX_ERROR;
         }
 
+        cache->sh->count++;
+
         ngx_memcpy((u_char *) &fcn->node.key, c->key, sizeof(ngx_rbtree_key_t));
 
         ngx_memcpy(fcn->key, &c->key[sizeof(ngx_rbtree_key_t)],