fix log message : argument was bytes not String

[aaujon]

Fix logger, error message was :

  File "/home/arnaud/.local/lib/python3.10/site-packages/caldav/davclient.py", line 77, in __init__
    "Expected some valid XML from the server, but got this: \n"
TypeError: can only concatenate str (not "bytes") to str

[tobixen]

While you're at it, a bit further up there is this one:

if content_length == 0 or not self._raw:

Perhaps this would be better:

if content_length == 0 or not self._raw.strip():

[tobixen]

Nevermind, I think I misunderstood it.

[aaujon]

Thanks for the quick merge :)