🩹 avoid passing second parameter to class_exists

[mikeyzm]

50d7a3f added provider class existence check, that would pass the key of app.providers as the second parameter to class_exists. 0 is a falsy value so class_exists does not check if the first provider class is autoloaded.

This PR uses closure instead of callable to avoid passing the second parameter to class_exists.

[QWp6t]

Do you want to also add a closure to ConfigCacheCommand?

[mikeyzm]

No. array_filter passes value as the only argument to callback by default.

Collection::filter calls array_filter with the option ARRAY_FILTER_USE_BOTH which passes both value and key.

[QWp6t]

Oh yeah, of course. Good catch.