patch 8.0.0983: unnecessary check for NULL pointer

Problem:    Unnecessary check for NULL pointer.
Solution:   Remove the NULL check in dialog_changed(), it already happens in
            dialog_msg(). (Ken Takata)
diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
index 8ca11f0..3682e79 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -1981,9 +1981,7 @@
     buf_T	*buf2;
     exarg_T     ea;
 
-    dialog_msg(buff, _("Save changes to \"%s\"?"),
-			(buf->b_fname != NULL) ?
-			buf->b_fname : (char_u *)_("Untitled"));
+    dialog_msg(buff, _("Save changes to \"%s\"?"), buf->b_fname);
     if (checkall)
 	ret = vim_dialog_yesnoallcancel(VIM_QUESTION, NULL, buff, 1);
     else