And log the correct number in the error case.

BSP now does this, so update our implementation to match.

git rid of uint and ulong

- combine the two context structs and pass wf_ctx everywhere
- rename wf -> wf_file and constify it
- factor out pvi_wf_get_temp_index

this originally appeared to be dead code, but it writes to `wf_table`
through the global variable `waveformdata`.