Create Sample error
@igboyes 
After the latest fix, I seem to get the following error:
```
"POST /api/samples HTTP/1.1" 201 
Traceback (most recent call last):
  File "/home/naomis/Projects/virtool/virtool/jobs/job.py", line 75, in run method()
  File "/home/naomis/Projects/virtool/virtool/jobs/create_sample.py", line 96, in make_sample_dir analysis_path = os.path.join(self.sample_path, "analysis")
  File "/home/naomis/.virtualenvs/virtool/lib/python3.6/posixpath.py", line 80, in join a = os.fspath(a)
TypeError: expected str, bytes or os.PathLike object, not NoneType

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.6/multiprocessing/process.py", line 258, in _bootstrap self.run()
  File "/home/naomis/Projects/virtool/virtool/jobs/job.py", line 87, in run self.cleanup()
  File "/home/naomis/Projects/virtool/virtool/jobs/create_sample.py", line 318, in cleanup
    for file_id in self.files:
TypeError: 'NoneType' object is not iterable

```
diff --git a/virtool/jobs/create_sample.py b/virtool/jobs/create_sample.py
index dd2038597..d2dbde41e 100644
--- a/virtool/jobs/create_sample.py
+++ b/virtool/jobs/create_sample.py
@@ -51,6 +51,7 @@ class CreateSample(virtool.jobs.job.Job):
 
         #: The ordered list of :ref:`stage methods <stage-methods>` that are called by the job.
         self._stage_list = [
+            self.check_db,
             self.make_sample_dir,
             self.trim_reads,
             self.save_trimmed,
['virtool/jobs/create_sample.py']