DXF unicode encoded layer names should not raise an exception

[chungkang]

Describe the bug
When I'm trying to read dxf file which includes German Umlauts(ä, ö, ü) letters in layer name, it shows the error below.

To Reproduce
Information and data needed to reproduce the error:

1. A simplified Python script which triggers the error.
   doc = ezdxf.readfile("umlaut_layer_test.dxf")

2. Information about the ezdxf version and the OS.
   dzdxf 0.17.2 / Window 11

3. If a 3rd party DXF file causes the error, add a simplified and zipped
   dxf

Expected behavior
Checking the error when reading the letter Umlauts ü(Unicode Character: \U+00FC)

[mozman]

Can not download and open your DXF file!

This works in the current version of ezdxf:

[mozman]

The recover module decodes the DXF unicode encoding: \U+00FC -> ü

Documentation of the recover module: https://ezdxf.mozman.at/docs/drawing/recover.html

[chungkang]

recover module works well. Thanks