patch 8.1.1374: check for file changed triggers too often

Problem:    Check for file changed triggers too often.
Solution:   Don't use "b_p_ar" when it is negative.
diff --git a/src/fileio.c b/src/fileio.c
index 4d9cd05..c9387ce 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -6776,7 +6776,7 @@
 	{
 	    // When 'autoread' is set we'll check the file again to see if it
 	    // re-appears.
-	    buf->b_mtime = buf->b_p_ar;
+	    buf->b_mtime = (buf->b_p_ar >= 0 ? buf->b_p_ar : p_ar);
 	    buf->b_orig_size = 0;
 	    buf->b_orig_mode = 0;
 	}
diff --git a/src/version.c b/src/version.c
index b3ecd8b..e8da844 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1374,
+/**/
     1373,
 /**/
     1372,