StackedDiscreteBar: Negative values lead to incorrect bar placement

[sophiamersmann]

Description

• This chart looks broken because one of the indicators (Land use change) has negative values that stacked discrete bar charts don't support
• This leads to incorrect bar placements

Expected behaviour

• In the long term, we should probably support negative values for (discrete) stacked bar charts (see #1166)
• For now, we should make sure that negative values don't break the chart (probably by ignoring them)

Steps to reproduce

1. Go to https://ourworldindata.org/grapher/food-emissions-supply-chain?country=Apples~Bananas
2. Note that bars overflow
3. Hover over one of the bars
4. Note that Land use change has a negative value

Screenshots