patch 9.0.0509: confusing error for "saveas" command with "nofile" buffer

Problem:    Confusing error for "saveas" command with "nofile" buffer.
Solution:   Give a clearer error message. (closes #11171)
diff --git a/src/bufwrite.c b/src/bufwrite.c
index b283b5e..3ff7fb3 100644
--- a/src/bufwrite.c
+++ b/src/bufwrite.c
@@ -888,7 +888,8 @@
 	    --no_wait_return;
 	    msg_scroll = msg_save;
 	    if (nofile_err)
-		emsg(_(e_no_matching_autocommands_for_acwrite_buffer));
+		semsg(_(e_no_matching_autocommands_for_buftype_str_buffer),
+							       curbuf->b_p_bt);
 
 	    if (nofile_err
 #ifdef FEAT_EVAL