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/buffer.c b/src/buffer.c
index 6bcd28b..2ca131d 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1035,7 +1035,14 @@
 	    buf = old_curbuf->br_buf;
 	if (buf != NULL)
 	{
+	    int old_msg_silent = msg_silent;
+
+	    if (shortmess(SHM_FILEINFO))
+		msg_silent = 1;  // prevent fileinfo message
 	    enter_buffer(buf);
+	    // restore msg_silent, so that the command line will be shown
+	    msg_silent = old_msg_silent;
+
 # ifdef FEAT_SYN_HL
 	    if (old_tw != curbuf->b_p_tw)
 		check_colorcolumn(curwin);