idevicebackup: Give the device time to prepare backup data
idevicebackup: Give the device time to prepare backup data

This change requests the initial backup files more gracefully as
the device might need more time to prepare the backup data for
bigger backups. Otherwise we cause a crash by attempting to parse
a plist message we did not receive yet when the device is busy.

upbit/libimobiledevice,Tatsh/libimobiledevice,patweb/libimobiledevice,patweb/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice-win32/libimobiledevice,upbit/libimobiledevice,kalev/libimobiledevice,Tatsh/libimobiledevice,kalev/libimobiledevice,upbit/libimobiledevice,kalev/libimobiledevice,libimobiledevice/libimobiledevice,patweb/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice/libimobiledevice,libimobiledevice-win32/libimobiledevice