Fix map navigation on some android native browsers

Mouse move event is triggered only once on some android browser, for example on Galaxy Tab P3110 + Android 4.1.1

I think it's related to these bugs: 
https://code.google.com/p/android/issues/detail?id=5491
https://code.google.com/p/android/issues/detail?id=19827

Prevent default mouse event behavior fixes the issue.