tng_num_frames_get reports incorrect num frames
I've converted a TRR & TPR to TNG (all attached) using trjconv. There should be 3 frames - tng_num_frames_get says there's 50,001.
I've started digging a little..
n_frames here is 50,000, which is the MD step number of the final frame.
I'm not sure if this is a bug with creating the TNG file (ie it's written wrong by trjconv), or if it's being read incorrectly.