let-bindings in pattern guards breaks indention

If one uses let bindings in pattern guards, the indention detection is completely borked.

If in the example below one presses RET at the marked position, you end up all the way to the left.

Expected behavior is that it keeps the indention of the curly braces (as it would if the let binding is dropped)
```
debugActions conf
| let mask = modMask conf
= [ RA { -- Curser here, press RET
}
]
```