ublox: return error when no bands are parsed

If load_current_bands_finish() returns a NULL GArray, we must set the
GError or otherwise the daemon will segfault when the caller
dereferences the GError:

    current_bands = MM_IFACE_MODEM_GET_INTERFACE (self)->load_current_bands_finish (self, res, &error);
    if (!current_bands) {
        /* Errors when getting current bands won't be critical */
        mm_warn ("couldn't load current Bands: '%s'", error->message);
        g_error_free (error);
    }

This may happen with an empty but balid +UACT response, e.g.:
   AT+UACT?
   +UACT: ,,,
   OK

Or when it replies a full empty string:
   AT+UACT?
   OK

0 files changed, 0 insertions, 0 deletions