do not set file time in ngx_copy_file() if the time is -1,
this fixes an issue when file is moved across devices

src/core/ngx_file.c

diff --git a/src/core/ngx_file.c b/src/core/ngx_file.c
index 6844849..b5160f3 100644
--- a/src/core/ngx_file.c
+++ b/src/core/ngx_file.c
@@ -762,10 +762,12 @@
         size -= n;
     }
 
-    if (ngx_set_file_time(to, nfd, cf->time) != NGX_OK) {
-        ngx_log_error(NGX_LOG_ALERT, cf->log, ngx_errno,
-                      ngx_set_file_time_n " \"%s\" failed", to);
-        goto failed;
+    if (cf->time != -1) {
+        if (ngx_set_file_time(to, nfd, cf->time) != NGX_OK) {
+            ngx_log_error(NGX_LOG_ALERT, cf->log, ngx_errno,
+                          ngx_set_file_time_n " \"%s\" failed", to);
+            goto failed;
+        }
     }
 
     rc = NGX_OK;