check-sof-logger: fail on empty logs

[marc-hb]

1st commit:

fix some quoting and rephrase some errors
Get the number of shellcheck warnings down a bit.

2nd commit:

fail when there's only the header
Found by chance while testing Zephyr.

[marc-hb]

https://github.com/thesofproject/sof-test/pull/629/checks?check_run_id=2100354934 has fewer shellcheck failures than before.

Interesting: the added test does fail on https://sof-ci.01.org/softestpr/PR629/build609/devicetest/?model=BYT_MB_NOCODEC&testcase=check-sof-logger

2021-03-13 02:55:42 UTC [REMOTE_ERROR] Nothing but the header in /home/ubuntu/sof-test/logs/check-sof-logger/2021-03-13-02:55:33-7598/logger.data.log

In the same run, https://sof-ci.01.org/softestpr/PR629/build609/devicetest/?model=BYT_MB_NOCODEC&testcase=check-playback-10sec has logs on the same system so the logger is not completely broken as it was in #294 / #297

[marc-hb]

github fix superseded by PR 630

[marc-hb]

SOFCI TEST

[marc-hb]

https://sof-ci.01.org/softestpr/PR629/build610/devicetest/?model=BYT_MB_NOCODEC&testcase=check-sof-logger failed the exact same so this is deterministic.

[marc-hb]

I took a longer look at the code and at #161 and #167 and realized the logic of this test does not make any sense.

There's an initial shellcheck cleanup without any functional change submitted in #659. Then I will submit a proper refactoring.