Fixes popup when zooming using only one finger.

When a user was zooming using the "double tap and while holding swipe
up/down" gesture, the "Open/Download/New Tab" dialog would be shown,
ending the zooming gesture, what made zooming using that gesture
impossible. This commit fixed that issue.
Merge pull request #3 from karolba/no-popup-while-zooming

Fixes popup when zooming using only one finger.