Fixed a release-only crash when showing the New Withdrawal screen.

The linker was  removing the CursorWrapper type in Release because it's not staticlly referneced
anywhere, so using data.JavaCast<ICursor>() instead of (ICursor)data avoids the problem.

I could have added a static reference to the CursorWrapper instead to make the linker keep it. E.g.

static bool falseflag = false;
static MyActivity ()
{
	if (falseflag) {
		var c = new CursorWrapper(null);
	}
}

More info on the linker issue: https://bugzilla.xamarin.com/show_bug.cgi?id=8313