graftExpr produces bad output for list literals

```haskell
module Test where

import Data.Generics
import Development.IDE.GHC.Compat (GenLocated(L), Located)


data Blah = Blah (Located [Located String])

blah :: Located Blah
blah = L _ (Blah (L _ [_, _]))
```

refining the hole at `[_,` produces the output 

```haskell
blah = L _ (Blah (L _ [L _ _ _]))
```

where the `,` got swallowed!