Consecutive \grace music

[Dan Eble]

```
\version "2.20.0"
{ \grace c8 \grace d8 e4 }

```

That crashes.  The oldest version I tried was 2.20, but I suspect the problem 
is ancient.  Does anyone disagree that the above would ideally be treated as if 
it were this?

```
{ \grace { c8 d8 } e4 }
```

Regards,
— 
Dan