improve error when there are no files that passed human-filtering

[antgonza]

If one of the projects has no reads passing human-filtering, the error is:

File "/home/qiita/miniconda3/envs/qp-knight-lab-processing-2022.03/bin/seqpro", line 33, in
sys.exit(load_entry_point('metapool', 'console_scripts', 'seqpro')())
File "/home/qiita/miniconda3/envs/qp-knight-lab-processing-2022.03/lib/python3.9/site-packages/click/core.py", line 1130, in __call__
return self.main(*args, **kwargs)
File "/home/qiita/miniconda3/envs/qp-knight-lab-processing-2022.03/lib/python3.9/site-packages/click/core.py", line 1055, in main
rv = self.invoke(ctx)
File "/home/qiita/miniconda3/envs/qp-knight-lab-processing-2022.03/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/qiita/miniconda3/envs/qp-knight-lab-processing-2022.03/lib/python3.9/site-packages/click/core.py", line 760, in invoke
return __callback(*args, **kwargs)
File "/home/qiita/qiita_spots/metagenomics_pooling_notebook/metapool/scripts/seqpro.py", line 52, in format_preparation_files
preps, us, uf = preparations_for_run(run_dir,
File "/home/qiita/qiita_spots/metagenomics_pooling_notebook/metapool/prep.py", line 425, in preparations_for_run
sample_files = fastq_files_found[project]
KeyError: '[project_name]'

replacing the actual project name for [project_name]