patch 7.4.1662
Problem:    No test for an invalid Ex command on a channel.
Solution:   Test handling an invalid command gracefully.  Avoid getting an
            error message, do write it to the channel log.
diff --git a/src/channel.c b/src/channel.c
index 64393f9..22f63b3 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -1661,8 +1661,17 @@
 
     if (STRCMP(cmd, "ex") == 0)
     {
+	int save_called_emsg = called_emsg;
+
+	called_emsg = FALSE;
 	ch_logs(channel, "Executing ex command '%s'", (char *)arg);
+	++emsg_silent;
 	do_cmdline_cmd(arg);
+	--emsg_silent;
+	if (called_emsg)
+	    ch_logs(channel, "Ex command error: '%s'",
+					  (char *)get_vim_var_str(VV_ERRMSG));
+	called_emsg = save_called_emsg;
     }
     else if (STRCMP(cmd, "normal") == 0)
     {