Added check to see if we were zooming before swallowing the canvas scroll event.

src/viewer.js

@@ -2847,9 +2847,12 @@ function onCanvasScroll( event ) {
         }
     }
     else {
+        gestureSettings = this.gestureSettingsByDeviceType( event.pointerType );
+        if (gestureSettings && gestureSettings.scrollToZoom) {
             return false;   // We are swallowing this event
         }
     }
+}
 
 function onContainerEnter( event ) {
     THIS[ this.hash ].mouseInside = true;