Fixed all count() calls inside loops

[sreichel]

Description

#15507

This improves the performance of a few loops which were running count() in every iteration.

Fixes all others.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

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[orlangur]

@sreichel such change does not affect performance in fact, please check #16027 (comment) for more details.