fix zoom-in/zoom-out using mouse wheel

regression introduced by 2393:235f847be37e "python3 support: pylint, W1619 #(old-division) division w/o __future__ statement"

<?xml version='1.0' encoding='utf-8'?>
<BeremizRoot xmlns:xsd="http://www.w3.org/2001/XMLSchema" URI_location="LOCAL://">
  <TargetType/>
</BeremizRoot>