formatter crash

[rszyma]

panicked at src/formatter/use_defsrc_layout_on_deflayers.rs:252:34:
line comment inside deflayer should always have newline

this config causes crash:

(defsrc
  a b c
)
(deflayer base
  a b ;;
  c
)

while this doesn't:

(defsrc
  a b c
)
(deflayer base
  a b ;;
  c)