A bad sample in a qiime artifact prevents the other samples from being processed

[arivers]

A QIIME2 user reported that when they ran their .qza file through itsxpress they received an error about clustering. What happened was they had a bad fastq file which had no reads after merging. Rather than telling them this and processing the next file, Q2-ITSxpress stopped and passed along the underlying error.

The fix should be to:

1. provide the user with in formation about what sample failed
2. continue processing the next sample.