Fix for -10% and +10% buttons in station's lobby

[Max5377]

Fixes #5585

The problem was with this line in refuelInternalTank in data/pigui/modules/station-view/01-lobby.lua:

station:AddCommodityStock(Commodities.hydrogen, -math.ceil(mass))

math.ceil is rounding number up, so if this number is negative(ex. -2.3) it will be rounded to -2 because it is nearest value that greater or equal to -2.3. So the solution is to change above mentioned line to:

local commodityChangeAmount = mass < 0 and math.floor(mass) or math.ceil(mass) station:AddCommodityStock(Commodities.hydrogen, commodityChangeAmount)

Accepted answer by Guffa(albeit it's for javascript, but works the same way)

[impaktor]

Looking good

Just change

Fix for #5585

to

Fixes #5585

and it will auto-close the issue when we merge this code.

[Max5377]

@impaktor Done

[Max5377]

Upon futher testing, I can say that my solution is not good either.
In my code, the station will receive more hydrogen than needed, because number is just rounded up, leaving fractional parts behind. Example:
Coronatrix fuel tank: 23t
10% from this amount: 2.3t

math.floor(-2.3) = -3, math.ceil(2.3) = 3

In the original code, it would be a little different:

math.ceil(-2.3) = -2, math.ceil(2.3) = 3

So, if there are no fractions in the goods, I don't think this can be correctly counted without them. That's what I think, at least.

Also, in this line:

station:AddCommodityStock(Commodities.hydrogen, commodityChangeAmount)

I forgot to add minus to commodityChangeAmount, because of this, demand and in stock decrease is mixed up (-10% decreases in stock and +10% decreases demand).

[impaktor]

@Max5377 I suggest you start a new branch & PR fixing the minus, and any other relevant issue as you've described.

[Max5377]

@impaktor I will definitely fix the minus part. As for the other thing, I don't know how to fix that, without fractional parts in the goods.