Incorrect UPnP class for unofficial subclass

[amelchio]

I think that I found a regression with #713. When I have a favorite like this:

<DIDL-Lite xmlns="urn:schemas-upnp-org:metadata-1-0/DIDL-Lite/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:r="urn:schemas-rinconnetworks-com:metadata-1-0/" xmlns:upnp="urn:schemas-upnp-org:metadata-1-0/upnp/">
  <item id="10092020urn%3adr%3amu%3achannel%3a4f3b8911860d9a33ccfdaf41" parentID="10fe2064live%3adistrict%3ap4" restricted="true">
    <dc:title>DR P4 Fyn</dc:title>
    <upnp:class>object.item.audioItem.audioBroadcast.#channel</upnp:class>
    <desc id="cdudn" nameSpace="urn:schemas-rinconnetworks-com:metadata-1-0/">SA_RINCON74247_</desc>
  </item>
</DIDL-Lite>

and I try to use it like this:

python -c 'import soco; print(soco.SoCo("10.0.2.14").music_library.get_sonos_favorites()[9].reference.resources)'

I get this error:

soco.exceptions.DIDLMetadataError: UPnP class is incorrect. Expected 'object.item.audioItem.audioBroadcast.channel', got 'object.item.audioItem.audioBroadcast'

I have found this to be due to different handling of .#:

SoCo/soco/data_structures.py

Lines 84 to 86 in 508cb1e

	# Certain music services has been observed to sub-class via a .# syntax
	# instead of just . we simply replace it with the official syntax
	didl_class = didl_class.replace(".#", ".")

SoCo/soco/data_structures.py

Lines 568 to 571 in 508cb1e

	# In case this class has an # specified unofficial
	# subclass, ignore it by stripping it from item_class
	if ".#" in item_class:
	item_class = item_class[: item_class.find(".#")]

I was able to fix my test case by making either of those work like the other. However, I am not sure what exactly is happening or what the right path forward would be?