Make non-hybrid visualization work with hybrid schedules

Use-case: A chevron or spectroscopy experiment. User adds gates (operations with gate info) and pulses (operations with pulse info) to a schedule and tries to visualize this using the circuit diagram visualization.

Currently this gives an exception that is impossible to understand without a deep understanding of the internals (which puzzled @jgloudemans and myself). The feature is working as it is intended, but is so confusing that it will scare away users. Before introducing a proper solution (see #6 (closed) ) it is worthwhile to make the process less painful.