[patch] CTRL Click on units fails to check for existing orde

[alex6]

Hello everybody !

I'm new in this forum and i'm one of those who played the original transport tycoon in the nineties.
So many hours playing with that game so addictive.

I found the OpenTTD version several years ago and i was glad to find and play at the game once again.

As i enjoy this game, i'd like to contribute to the new features and bugs correcting.

So i suggest this patch from the bug report (https://bugs.openttd.org/task/5990?project=1&pagenum=3).

When the user wants to share orders from a vehicle with another (Ctrl+Click on the other vehicle), if there are orders already given to this vehicle,
the orders are overwritten without any warning.
The patch just add a warning message for the user to confirm (or not) the action.