For some reason when Picard doesn't detect a CD drive it incorrectly displays an error message saying "module 'libdiscid.compat.discid' has no attribute 'disc'", when it should print the line from the first exception because that's actually useful.

Example debug log:

```
D: 20:38:14,061 /usr/lib/picard/picard/disc.read:63: Reading CD using device: b'/dev/cdrom'
E: 20:38:14,065 /usr/lib/picard/picard/util/thread.run:64: Traceback (most recent call last):
 File "/usr/lib/picard/picard/disc.py", line 65, in read
   disc = discid.read(device, features=['mcn'])
 File "/usr/lib/python3/dist-packages/libdiscid/compat/discid.py", line 176, in read
   map(lambda feature: _decode(feature, 'ascii'), features))
 File "/usr/lib/python3/dist-packages/libdiscid/compat/discid.py", line 111, in read
   ), 0))
 File "/usr/lib/python3/dist-packages/libdiscid/_init_.py", line 260, in read
   disc.read(device, features)
 File "libdiscid/_discid.pyx", line 92, in libdiscid._discid.DiscId.read
 File "libdiscid/_discid.pyx", line 70, in libdiscid._discid.DiscId._read
libdiscid.exceptions.DiscError: cannot open device `/dev/cdrom'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
 File "/usr/lib/picard/picard/util/thread.py", line 60, in run
   result = self.func()
 File "/usr/lib/picard/picard/disc.py", line 70, in read
   except discid.disc.DiscError as e:
AttributeError: module 'libdiscid.compat.discid' has no attribute 'disc'
```