Don't center map when user wants to zoom but zoom doesn't change

[djasa]

1. zoom out to minimum zoom (zoom=5 with current map)
2. move cursor somewhere near the edge of the map
3. turn mouse wheel down to zoom further out

what happens: map is not zoomed out but it is centered around would-be new center of the would-be new viewport

what should happen: since map can't fullfill the request, no-op should be performed