[deviantart] improve handling of private deviations (#414)

- don't try to call '/deviation/metadata' with an empty list of
  deviation ids
- print a warning when detecting private deviations without having
  a 'refresh-token'

gallery_dl/version.py

@@ -6,4 +6,4 @@
 # it under the terms of the GNU General Public License version 2 as
 # published by the Free Software Foundation.
 
-__version__ = "1.10.4"
+__version__ = "1.10.5-dev"