do not clean cache if memory cache keys zone is cold

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 0c2b9e2..8063648 100644
--- a/src/http/ngx_http_file_cache.c
+++ b/src/http/ngx_http_file_cache.c
@@ -895,8 +895,9 @@
 
     now = ngx_time();
 
-    if (now >= cache->next_clean_time) {
-
+    if (now >= cache->next_clean_time
+        && now >= cache->created + cache->inactive)
+    {
         ngx_log_error(NGX_LOG_NOTICE, ngx_cycle->log, 0,
                       "clean unused cache files");