PVS-Studio warning V595 for Newton Game Dynamics

void
ptw32_throw (DWORD exception)
{
  ....
  ptw32_thread_t * sp =
    (ptw32_thread_t *) pthread_getspecific (ptw32_selfThreadKey);

  sp->state = PThreadStateExiting;

  if (exception != PTW32_EPS_CANCEL &&
      exception != PTW32_EPS_EXIT)
  {
    exit (1);
  }
  ....
  if (NULL == sp || sp->implicit)
  ....
}

This suspicious code was found in Newton Game Dynamics project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'sp' pointer was utilized before it was verified against nullptr. Check lines: 77, 85. ptw32_throw.c 77

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