userpref: [GnuTLS] Fix pairing record generation and improve error handling
userpref: [GnuTLS] Fix pairing record generation and improve error handling

In newer GnuTLS versions the parameters supplied to
gnutls_x509_privkey_import_rsa_raw() are actually checked for somewhat
sane values. Since we were passing the same values for all parameters,
this check fails and the device certificate is never generated.
However due to missing checks the pairing record was saved anyway, with
an empty device certificate. This led to TLS errors during communication,
leading to the "GnuTLS: Error in pull function" error message appearing
and the communication to fail.
This commit fixes the issue by passing some sane values, and also improves
the overall error handling during generation of the paring record.

Tatsh/libimobiledevice,libimobiledevice-win32/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice/libimobiledevice,Tatsh/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice-win32/libimobiledevice