Cherry-pick #25357 to 7.x: Fix s3 input when there is a blank line in the log file

[kaiyan-sheng]

Cherry-pick of PR #25357 to 7.x branch. Original message:

What does this PR do?

When there is an empty line in a log file, s3 input shouldn't abort the rest of the file. This PR is to skip the empty line and continue to ingest the rest of the log file.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Closes S3 collector aborts when there is a blank line in the log file #24872

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Pinging @elastic/integrations (Team:Integrations)

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Build stats

• Build Cause: Pull request #25414 opened

• Start Time: 2021-04-28T22:37:40.783+0000

• Duration: 52 min 46 sec

• Commit: d53d648

Test stats 🧪

Test	Results
Failed	0
Passed	6980
Skipped	1193
Total	8173

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Test stats 🧪

Test	Results
Failed	0
Passed	6980
Skipped	1193
Total	8173