xmlrpc: do not raise if jobs.list is empty

The API should just return an empty list.

Reported-by: Dave Pigott <dave.pigott@linaro.org>
Signed-off-by: Rémi Duraffort <remi.duraffort@linaro.org>
15 jobs for <span class="ref-name">api-jobs-list-404</span> in 36 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #32534
amd64
dispatcher-debian-10

00:04:10

passed #32532
amd64
dispatcher-debian-9

00:03:39

passed #32535
amd64
server-debian-10

00:02:57

passed #32533
amd64
server-debian-9

00:03:28

 
  Analyze
passed #32536
amd64
black

00:01:13

passed #32538
amd64
code_quality

00:00:57

passed #32537
amd64
codestyle

00:01:02

passed #32541
amd64
job-schema

00:02:45

passed #32539
amd64
pylint

00:03:24

failed #32540
dind amd64 allowed to fail
sast

00:25:31

 
  Build
passed #32544
amd64
amd64/pkg-debian-10

00:02:04

passed #32543
amd64
amd64/pkg-debian-9

00:02:18

passed #32542
amd64
doc

00:02:19

 
  Docker
passed #32545
dind amd64
amd64/lava-dispatcher

00:01:44

passed #32546
dind amd64
amd64/lava-server

00:03:19

 
Name Stage Failure
failed
sast Analyze
257e8c647a3e: Pull complete
Digest: sha256:30db5c0211cf38fd8e355782ef02931323a6bb62cd7543afa92249a1f2f109cd
Status: Downloaded newer image for registry.gitlab.com/gitlab-org/security-products/analyzers/find-sec-bugs-gradle:2
2019/03/13 11:34:55 Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
2019/03/13 11:34:55 Timeout when running the analyzer
Uploading artifacts...
WARNING: gl-sast-report.json: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1