Disambigue refill vehicle

This is a bug fix.
I don't know if there a issue for that bug...
When you try to refill square with 2 or more fuel tanks, only first will be refilled.
It's easy to reproduce with debug menu:
1. Spawn Motocycle, hose, steel jerrycan.
2. Siphon all gasoline
3. Turn lights on.
3. Wait 1800 bits. (need to spend some batteries)
4. Set cursor to ^
5. Try to refill.
... Try to reflll.
There is no way to refill motocycle from jerrycan.

So this PR fix this bug.
If square got only one valid fuel tank, it refill it silently.
if tanks > 1, then selection menu will be created.