Error message unclear when filtering and "printing" in same CLI command if no passing ligands

[maylinnp]

If no ligands pass a filter, and e.g., SDF file writing is requested in the same command, it will error because the bookmark does not exist. It does not make it clear that the bookmark does not exist, because no ligands passed filter. It's not technically an error that no ligands passed a filter, but it should make that fact more clear before failing to write SDF files. Error handling could be more clear in general on which API method fails.