style: cppcheck — const-correctness in file_send_special and test_chunk

file_send_special now takes const File*; test_chunk declares the deserialized
Chunk* const.  cppcheck (--error-exitcode=1) now exits clean; clang-format
clean; unit 29/29.

tests/test_chunk.c

@@ -273,9 +273,8 @@ static void test_chunk_special_rdev_out_of_range_rejected() {
   EXPECT_NOT_NULL(chunk);
   Data* serialized = chunk_serialize(chunk, true);
   EXPECT_NOT_NULL(serialized);
-  Chunk* deserialized = chunk_deserialize(serialized, true);
+  const Chunk* deserialized = chunk_deserialize(serialized, true);
   EXPECT_NULL(deserialized);
-
   data_destroy(serialized);
   chunk_destroy(chunk);
 }