Allow to create item-proxy-requests on entity-ghost

[protocol_1903]

Currently, if you attempt to create an item-proxy-request on an entity-ghost it will crash the game, stating that the target entity must have health. I would rather it create a ghost proxy-request (like those created from placing blueprints with modules, train fuel, etc.) instead of crashing. Alternatively, if this is already a feature and I'm doing it wrong, please let me know.

The use case for this is trains. I'm working on a mod to have trains request fuel when created, but as soon as a train is created it will be switched to automatic mode IF there is not a fuel request. If so, it would wait for the fuel, then switch to auto. Which is great, except I can't create the fuel request until after the entity has been created, but then it's already in auto mode, so i need to make it manual, then turn it back to auto... A lot of work to get it to stay put.

[curiosity]

It's part of the ghost itself.