Fix panic in labels debug message

[adityacs]

Just a placeholder for now. Need to test more

What this PR does / why we need it:
Fix panic in labels debug message

Which issue(s) this PR fixes:
Fixes #1680

[codecov-io]

Codecov Report

Merging #1687 into master will increase coverage by 0.79%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master    #1687      +/-   ##
==========================================
+ Coverage   63.27%   64.07%   +0.79%     
==========================================
  Files         121      121              
  Lines        9027     9027              
==========================================
+ Hits         5712     5784      +72     
+ Misses       2897     2841      -56     
+ Partials      418      402      -16

Impacted Files	Coverage Δ
pkg/logentry/stages/timestamp.go	87.34% <100%> (+10.12%)	⬆️
pkg/logentry/stages/regex.go	78.57% <100%> (+17.85%)	⬆️
pkg/logentry/stages/output.go	75.75% <100%> (+18.18%)	⬆️
pkg/logentry/stages/tenant.go	95.12% <100%> (+14.63%)	⬆️
pkg/logentry/stages/template.go	86.66% <100%> (+17.77%)	⬆️
pkg/logentry/stages/labels.go	78.94% <100%> (+10.52%)	⬆️
pkg/logentry/stages/metrics.go	59.89% <66.66%> (+7.69%)	⬆️
pkg/promtail/targets/tailer.go	75.86% <0%> (-2.3%)	⬇️
pkg/ingester/transfer.go	66.42% <0%> (+1.42%)	⬆️
... and 10 more

[owen-d]

Thanks for tracking this down! I agree with @cyriltovena, lets add a small test for this then LGTM.

[adityacs]

@owen-d @cyriltovena need a small clarity. Just wanted to know what's the take here. Should we just remove .String() from reflect.TypeOf(lValue).String() in all Debug lines ?
OR
should we set extracted[n] = "" here https://github.com/grafana/loki/blob/master/pkg/logentry/stages/json.go#L153 ?

[cyriltovena]

I think removing the .String() is a good idea. Pretty sure the logger will be fine, but the best option is to have a test covering this line/case.

[cyriltovena]

LGTM