cleanup new sample entry creation in mp4mx
cleanup new sample entry creation in mp4mx

gpac/gpac,gpac/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,gpac/gpac,gpac/gpac,rbouqueau/gpac,rbouqueau/gpac,rbouqueau/gpac,gpac/gpac,rbouqueau/gpac,gpac/gpac,rbouqueau/gpac,gpac/gpac,rbouqueau/gpac