Don't display/log an error message if text/menu/logon.* doesn't exist

For Wildcat (N)ewsletter command and PCBoard "NEWS" command, display
"No news is good news." instead. :-)

exec/pcboard.src

@@ -244,7 +244,10 @@ cmdstr CHAT
 	end_cmd
 
 cmdstr NEWS
-	menu logon
+	chkfile "%zmenu/logon.*"
+	if_true
+		menu logon
+		end_if
 	end_cmd
 
 cmdstr DOOR

exec/wildcat.src

@@ -48,7 +48,10 @@ cmdkey U
 	end_cmd
 
 cmdkey N
-	menu logon
+	chkfile "../text/menu/logon.*"
+	if_true
+		menu logon
+		end_if
 	pause
 	end_cmd