only 404-ban accounts with permission [gGh]:

never bonk anyone with read-access (able to see directory-listing)
or write-only (not able to retrieve any files at all) due to
either --ban-404 or --ban-url

fixes accidental ban when webdav-uploading files which
match any of the --ban-url patterns (#55)

also default-enables --ban-404 since it is now generally safe
(even when up2k is in turbo mode), plus make turbo smart enough to
disengage when necessary

copyparty/httpcli.py

@@ -655,6 +655,7 @@ class HttpCli(object):
                     and not body.startswith(b"<pre>source file busy")
                 )
             )
+            and (status != 404 or (self.can_get and not self.can_read))
         ):
             if status == 404:
                 g = self.conn.hsrv.g404