patch 8.1.0310: file info msg not always suppressed with 'F' in 'shortmess'

Problem:    File info message not always suppressed with 'F' in 'shortmess'.
            (Asheq Imran)
Solution:   Save and restore msg_silent. (Christian Brabandt, closes #3221)
diff --git a/src/memline.c b/src/memline.c
index fb262ac..fbdd8a3 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -828,10 +828,13 @@
  */
     void
 check_need_swap(
-    int	    newfile)		/* reading file into new buffer */
+    int	    newfile)		// reading file into new buffer
 {
+    int old_msg_silent = msg_silent; // might be reset by an E325 message
+
     if (curbuf->b_may_swap && (!curbuf->b_p_ro || !newfile))
 	ml_open_file(curbuf);
+    msg_silent = old_msg_silent;
 }
 
 /*