DSM file contains question marks instead of bytes

When decompiling the COFF file below, the produced `.dsm` file contains question marks instead of bytes.

## Input

```sh
$ decompile.sh x86-coff
```
where the input COFF file can be downloaded [here](https://github.com/avast-tl/retdec-regression-tests/raw/68e8849c1aba5a7a8592698ed56fe582ce087769/service/decompiler/recognition/x86-coff).

## Output

The produced `.dsm` file contains the following lines:
```
; section: .data
0xc0: ?? |? |
; section: .rdata
0xc0: ?? 63 6b 65 72 6d 61 6e 28 20 25 64 20 2c 20 25 |?ckerman( %d , %|
```

## Expected output

I would expect byte numbers instead of `??` and proper ASCII characters instead of `?` in between the pipes (`|`).

## Configuration

* Commit: 8c4b23dbbf0f2baaf6f2309fc189b054f58250ea (current `master`)
* 64b Arch Linux, GCC 7.2.1, Debug build of RetDec

Reproduce the problem with decompile.sh x86-coff using the linked COFF input and inspect the generated .dsm output for the .data and .rdata sections. Trace how bytes and ASCII text are rendered there, then verify that byte values and printable characters replace the question marks in the expected output.

Written by the indexing model from the issue text.