Some sessions have a missing, or broken samplerate value, causing the zoom-fit command to compute crazy h-scale values, resulting in asserts. The h-scale should be clamped to the zoom limits. zoom-fit should also do something sensible with the samplerate if it's undefined.
Fixed in a472a88
This was also (further?) fixed in 7831112753a3a419e328d7d6b0d474435a09d6ed.