zoom: Check the value of level before using it.

Check the value of level before dividing 1 by it.

Signed-off-by: Carlos Olmedo Escobar <carlos.olmedo.e@gmail.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>

src/zoom.c

@@ -120,12 +120,13 @@ weston_output_update_zoom_transform(struct weston_output *output)
 	float ratio, level;
 
 	level = output->zoom.spring_z.current;
-	ratio = 1 / level;
 
 	if (!output->zoom.active || level > output->zoom.max_level ||
 	    level == 0.0f)
 		return;
 
+	ratio = 1 / level;
+
 	if (wl_list_empty(&output->zoom.animation_xy.link))
 		zoom_area_center_from_pointer(output, &x, &y);