Check that sample-size estimation works without manifests

[vteague]

Sample size estimation will be done in a preliminary phase where counties upload preliminary cvrs but may not have a ballot manifest. The audit will not actually be started, but the process will run through the phases of setting the parameters and generating the assertions.

Check that nothing prevents reaching the assertion generation phase without manifests having been uploaded. There is no inherent reason that they should be necessary, but there may be some unexpected logic inside colorado-rla that makes this fail.