file.py task.py a some fuse failsafes.

If there are no files in the left in the sample_set don't request a
refuse.
Also add failsafe in the fuse, if for some reason a fuse is requested
but no results_files exist in the queries, don't run fuse and fail the
task

See #3621
3 jobs for <span class="ref-name">feature-s/3621-no_fuse_empty_set</span> in 13 minutes and 16 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test Tools
passed #201661
test_tools

00:00:06

 
  Test Unit
passed #201662
web
test_server_unit

00:00:18

 
  Test Functional
passed #201663
docker x86_64
test_server_functional

00:12:52