lockdown: Refactor pair record generation/loading logic a bit for efficiency
lockdown: Refactor pair record generation/loading logic a bit for efficiency

The current code always requests the public key and set's the SystemBUID, even
if a pair record already exists which has these values ready. The change moves
logic to only do that during generation of new certificates.

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