different deltas for glyphs with only missing components

In at least one case we have a font with a number of glyphs that have a single component, and that component is missing. We are computing different phantom points in this case.

Repro:

```
python3 -m ttx_diff 'https://github.com/googlefonts/parastoo-font?80a254f68a#sources/Parastoo.glyphspackage'
```

Start with the ttx_diff entry point and run the provided command against the pinned Parastoo.glyphspackage source. Trace how glyphs with a single missing component receive phantom points, then verify that these glyphs produce consistent deltas.

Written by the indexing model from the issue text.