patch 8.1.1379: filechanged test hangs

Problem:    Filechanged test hangs.
Solution:   Do not check 'autoread'.
diff --git a/src/fileio.c b/src/fileio.c
index b6a37f5..57c5f47 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -6774,9 +6774,8 @@
 	// FileChangedShell autocmd)
 	if (stat_res < 0)
 	{
-	    // When 'autoread' is set we'll check the file again to see if it
-	    // re-appears.
-	    buf->b_mtime = (buf->b_p_ar >= 0 ? buf->b_p_ar : p_ar);
+	    // Check the file again later to see if it re-appears.
+	    buf->b_mtime = -1;
 	    buf->b_orig_size = 0;
 	    buf->b_orig_mode = 0;
 	}