Undo "Go to depot" button

[eipi]

I've always missed a possibility to undo sending a convoy to the depot.
This small patch changes the behaviour of the "Go to depot" button. It is now possible to press the button again to send the convoy back to follow its original route.

[Yona-TYT]

Interesting..

[gauthier]

This is one of this very simple things whick make life much nicer. Thanks !

[prissi]

Thanks, in in r7044