Vehicle fuel indicators show confusing results as tanks are emptied.

Hey,

after some search I only found a brief mention about this in #12601
With the generic tanks the % indication for any liquid is quite unintuitive now...

probably known thing, I just can't find it in the issues so I thought I'll bring it up.
If you have two tanks with the same liquid both full you will get 100% indicators... As the liquid gets used from one of the tanks it drops correctly up to the 50% mark... At the point when one of the tanks is sucked dry, instead of getting less than 50%, the indicators jump up to 100%, because the empty tank is not included in the calculations...

Can we maybe keep the liquid tag on a tank even after being sucked dry? It might show e.g. 0.0L Diesel, but the player will be allowed to put in another liquid to change that to another liquid if he so desires.. basically it will merely indicate the original purpose of the tank.

Reproduce the issue with two generic tanks containing the same liquid, then trace the vehicle fuel-indicator calculation as one tank becomes empty. Done means the indicator continues to account for the emptied tank and reports the combined remaining amount without preventing that tank from being refilled with another liquid.

Written by the indexing model from the issue text.