AFURLSessionManager makes invalid initial upload/download task progress updates

AFURLSessionManager updates upload/download tasks' NSProgress instances in a way that generates an initial KVO notification for fractionCompleted value of 1.0 because totalUnitCount is 0 by the time completedUnitCount is set the first time. Expected initial value is 0.0. The fix was to swap setting completedUnitCount and totalUnitCount in all three places where it happens.