Fix flash of unstyled content on some sites

[Psychpsyo]

Fixes #769
This delays accessing window.innerHeight as that was causing the flash of unstyled content on the website.

Before fix:

After fix:

[FilipePS]

This modification doubles the execution time of the translationRoutine function.

From the original code, just place this line if (piecesToTranslate.length < 1) return; of code above the other const innerHeight = window.innerHeight;, and you will have the same result without affecting performance.

Do what I said and your pull request will be accepted.

[Psychpsyo]

Do what I said and your pull request will be accepted.

Done.

[FilipePS]

Thank you for your contribution.