VCD file without scope causes signals to be marked as "Not available" after reload
I happened to be generating VCD files without a scope in the signal definition. Loading such a file at first works as expected and I can add signals to the viewer. But reloading the file (no changes have happened to the file) causes signals in the viewer to be marked as "Not available". I manually edited the file, adding a scope around the signal definitions after which the file can be reloaded as expected and signals remain visible.
I don't know if not having a scope is a violation of the VCD format, but if it is it may be worth generating a warning when encountering such files?
Please find the two VCD files attached to reproduce. This behavior was present both on an older 0.3.0 build as well as the tip of main (v0.3.0-46-g71140aa).