Description: set zoomration

--- mirage-0.11.1.orig/mirage/__init__.py
+++ mirage-0.11.1/mirage/__init__.py
@@ -1430,6 +1430,7 @@ class Base(Gtk.Application):
                 print(traceback.format_exc(), file=sys.stderr)
         if self.vscroll.get_property("visible"):
             try:
+                zoomratio = float(self.currimg_width) / self.previmg_width
                 newvalue = abs(
                     self.layout.get_vadjustment().get_value() * zoomratio
                     + ((self.available_image_height()) * (zoomratio - 1)) // 2
