[BUG] convoys in replacement will give up replacement in some cases

[Mariculous]

What happened?
I had recently done a mass-replacement. Some Vehicles did not get replaced and had their "no load" state unchecked.

How to reproduce?
1. Load the attached save.
2. open the replacement dialogue of one of the vehicles.
3. check the "replace all" checkbox and set up some replacement, e.g. replace to 6 Friesians + Stage coach
4. click "full replace
5. Convoys won't find a depot as I removed it before. Note that the same will happen on large lines if there is no nearby depot at some point either.
6. Notice the "no load" will be unchecked, although on the server game I did also have some convoys idling around with "no load" still checked.
7. Build a depot
8. Notice that coaches won't attempt to enter that depot for replacement. The replacement remains set-up, however.

Expectations:
I'd expect the convoy to not clear the "no load" state if it didn't find a depot. At each stop I'd expect it to search for a depot for replacement.