Altered trading price strike-through line is invisible with "Programmer Art" resource pack enabled

The bug

The "Programmer Art" resource pack doesn't include a texture for the strike-through line used for altered prices in the trading GUI.

To reproduce

1. Enable the "Programmer Art" resource pack
2. Trade with a villager until it gives you a discount, or punch a villager so that it increases its prices
3. There will be two prices, none of them is striked through