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Account for fb2 books without covers

lector/guifunctions.py

@@ -14,12 +14,16 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import logging
+
 from PyQt5 import QtCore, QtGui, QtWidgets
 
 from lector import database
 from lector.settings import Settings
 from lector.resources import resources
 
+logger = logging.getLogger(__name__)
+
 
 class QImageFactory:
     def __init__(self, parent):