Avoid zero division in setup checks

[MichaIng]

Fixes: #30532

[MichaIng]

/backport to stable23

[solracsf]

Shouldn't it be !empty ? 🤔
Otherwise, you check if values are empty an then outputs a recommandation that they are full.

[MichaIng]

It's the free memory and the max cached keys (not the used memory/keys). In both cases, when they are null, nothing can be cached anymore, hence the warning as a performance recommendation makes sense. Not sure whether any max value can be actually set to 0 without disabling OPcache all together. However, it doesn't change something about the recommendation to always have 10% left free buffer, for interned strings, keys and overall OPcache size.

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Did some tests:

• opcache.memory_consumption cannot be set to 0, it will then use the minimum of 8 MiB.
• Same with opcache.max_accelerated_files, where the minimum of 223 cached keys is applied then.
• opcache.interned_strings_buffer=0 however is possible, which indeed disables the internet strings buffer completely so that $status['interned_strings_usage'] is not defined at all, which is probably the case with your setup @nursoda? It is now covered by this change.

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Drone failure is unrelated.

[MichaIng]

Another thing: Is there probably a flag for one of the CI checks/tools to fail on division by unverified variables?

[MichaIng]

jsunit failure is unrelated, same as here: #30557

[szaimen]

/rebase