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 URI_location="LOCAL://">
  <TargetType/>
  <Libraries Enable_Python_Library="true"/>
</BeremizRoot>