Fixed race condition with calculation for left and right coordinates …

[falkobuttler]

…of map view to calculate length

This caused the cell size sometimes to be 0 due to a race condition when converting coordinates from the map view to its super view. When that happened, all annotations become invisible. This constantly happens when rotating, especially in flyover mode.
Instead we are now calculating it against its own view, which always returns consistent and valid results.

[choefele]

Thanks for your PR. Could you please send me some step-by-step instructions how to reproduce the problem your are fixing with the sample app? I'd like to verify the solution of this issue. I'm not really sure how there would be a race condition around the super view of a view.

Also, [mapView convertPoint:CGPointZero toCoordinateFromView:mapView] in your code effectively makes this call redundant. My understanding is that the super view is required to convert the point into the correct coordinate system.

[choefele]

Also: your code causes the unit tests to fail because you changed the method parameters.