Mark to ligature positioning is not fully supported

I have UFO sources with the following lines in the features:

```
markClass uni0328 @bottom;
markClass uni0328 @ogonek;
```

This is quite natural so that the ogonek combines where appropriate with the letters that have the specific ogonek anchor and combines in the center with other letters. This compiles fine in fontmake.

However as soon as I add some mark to ligature code, e.g.:

```
pos ligature c_a.liga
mark @bottom
mark @top
mark @ogonek
ligComponent
mark @top
mark @bottom
mark @ogonek;
```

I get an error:

```
fontmake: Error: In 'FontFamily.designspace': Generating fonts from Designspace failed:
/FontFamily_Project/masters/FontFamily.ufo/features.fea:2605:1: Glyph uni0328 cannot
be in both @bottom and @ogonek
```