Fix star comment non-idempoteny

Previously, empty trailing lines in star comments would only get
stripped after the second formatting

src/Nixfmt/Lexer.hs

@@ -84,7 +84,16 @@ blockComment = try $ preLexeme $ do
   isDoc <- try ((True <$ char '*') <* notFollowedBy (char '/')) <|> pure False
 
   chars <- manyTill anySingle $ chunk "*/"
-  return $ PTBlockComment isDoc $ dropWhile Text.null $ fixIndent pos' $ removeStars pos' $ splitLines $ pack chars
+  return
+    . PTBlockComment isDoc
+    . dropWhile Text.null
+    . fixIndent pos'
+    . dropWhileEnd Text.null
+    . map Text.stripEnd
+    . removeStars pos'
+    . splitLines
+    . pack
+    $ chars
   where
     -- Normalize line ends and stuff
     splitLines :: Text -> [Text]

test/diff/comment/in.nix

@@ -42,6 +42,11 @@
   * test
   */
 
+ /* test
+  * test
+  *
+  */
+
   /*
    * FOO
    */

test/diff/comment/out.nix

@@ -36,6 +36,11 @@
     test
   */
 
+  /*
+    test
+    test
+  */
+
   # FOO
 
   /**