Sometimes, zeroing the width of mark glyphs does not work

Leaving as a note to self. I ran into this list of glyphs in a project where going Glyphs.app 2.x -> UFO does not zero the width of the glyph, meaning everything is shifted to the right. Need to figure out why.

```python
MARKS = [
"cha-khmer.below",
"co-khmer.below",
"co-khmer.below2",
"qa-khmer.below",
"qe-khmer.below",
"ta-khmer.below",
"ta-khmer.below2",
]
```