In VTM configuration, bitstreams generated previously not decodable in the current HEAD.

Using a VTM configuration file, i.e. either "cfg/encoder_intra_vtm.cfg" or "cfg/encoder_randomaccess_vtm.cfg" or "cfg/encoder_lowdelay_vtm.cfg", if a bitstream is generated using the code of Commit 877309ca, the decoding of this bitstream using the code of Commit 59e8ce06 (current HEAD) crashes. This is because, in Commit 70f4e327, a new SPS flag is not conditioned on the SPS flag "sps_nn_intra_pred_enabled_flag".