Fix a crash in job_log_incremental when a result line is too long

When a job log line is too long, the content is stripped and replaced by:
{"dt": "...", "lvl": "results", "msg": {"skip": "line way too long ..."}}.

Fix a crash when such log line is parsed.

See https://sentry.io/organizations/linaro/issues/1958935251

Signed-off-by: Rémi Duraffort <remi.duraffort@linaro.org>
16 jobs for fix-crash-with-long-results in 14 minutes and 10 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed #113641
amd64
dispatcher-debian-10

00:02:16

passed #113643
amd64
dispatcher-debian-11

00:02:41

passed #113642
amd64
server-debian-10

00:02:48

passed #113644
amd64
server-debian-11

00:04:57

 
  Analyze
passed #113645
amd64-dind
bandit-sast

00:00:50

passed #113646
amd64
black

00:00:33

passed #113647
amd64
code_quality

00:00:19

passed #113652
amd64
codespell

00:00:15

passed #113648
amd64
coverage

00:06:21

60.89%
passed #113649
amd64
dockerfiles

00:00:14

passed #113651
amd64
pylint

00:02:56

passed #113650
amd64
schemas

00:00:26

 
  Build
passed #113654
amd64
debian/10

00:01:46

passed #113653
amd64
doc

00:00:37

passed #113655
amd64-dind
docker-amd64-dispatcher

00:02:07

passed #113656
amd64-dind
docker-amd64-server

00:02:48