Fix prefix operator pattern-match invalid result

src-literatetests/15-regressions.blt

@@ -668,3 +668,7 @@ nand _ _         = True
 
 nor False False = True
 _ `nor` _       = False
+
+#test issue 256 prefix operator match
+
+f ((:) a as) = undefined

src/Language/Haskell/Brittany/Internal/Layouters/Pattern.hs

@@ -86,7 +86,7 @@ layoutPat (ghcDL -> lpat@(L _ pat)) = docWrapNode lpat $ case pat of
     --       return $ (x1' Seq.<| middle) Seq.|> xN'
   ConPatIn lname (PrefixCon args) -> do
     -- Abc a b c -> expr
-    let nameDoc = lrdrNameToText lname
+    nameDoc <- lrdrNameToTextAnn lname
     argDocs <- layoutPat `mapM` args
     if null argDocs
       then return <$> docLit nameDoc