fix: Adjust tailer loop criteria so it is actually re-tested

[paul1r]

What this PR does / why we need it:
A previous commit was made to adjust for a data race. This commit was incorrect in the sense that the criteria for exiting the loop was only set before starting the loop, and never actually retested.

This particular commit addresses that issue.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
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• If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[paul1r]

go test -race -count=1 ./pkg/querier
ok  	github.com/grafana/loki/v3/pkg/querier	2.497s

[ashwanthgoli]

lgtm