AGPUSH-1103 : Fix stats number for iOS and SPS

This fixes the bug of showing wrong numbers in the dashboard (on application level) for iOS and SPS variants. 
The fix works for SPS but I do not have access today to a mac. @cvasilak @edewit @matzew Could you give it a try ?
To reproduce it, you need to register at least 2 iOS devices to the same variant and then send some message.

This should go in master and 1.0.x branch
The `NotificationSenderCallback.onError` Implementation already logs a `warning`, that should be enough , no ?