fix(storage): add null check for $stream->getMetadata

[mateuszanella]

In the instance that a Stream object does not contain a wrapper_data metatada entry, the function returns null and throws the following exception when trying to read the size of the stream:

foreach() argument must be of type array|object, null given "exception":"[object] (ErrorException(code: 0): foreach() argument must be of type array|object, null given at /var/www/api/vendor/google/cloud-storage/src/ReadStream.php:63)

This PR introduces a simple check to see if the response from the metadata call is in fact an array, and returns 0 otherwise (following the default function behavior).

To be honest, I am not really sure why there is no size metadata for the stream, but I believe that this case should be handled, either by just returning 0 or by throwing a proper exception.

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[mateuszanella]

Perhaps is_iterable() would be best, but I'm open to feedback.

[Hectorhammett]

Hello @mateuszanella!

Thanks so much for your contribution. I think this is a simple fix, although we are missing the CLA. If we wish to merge this into the code, we require a signed CLA, more info here:
https://github.com/googleapis/google-cloud-php/blob/main/CONTRIBUTING.md

Other than that, it does look like a good and simple fix, but may I suggest if we can add a unit test for this to keep it consistent?

[mateuszanella]

Done :)

[bshaffer]

It would be better to call this is_null. We should be more specific with our handling. If something that isn't null and isn't an array is returned, it's okay if the function errors (because that case is unknown, and so we should handle it).

[mateuszanella]

Yeah, that makes sense. Fixed it!

[luizautentique]

very cool implementation @mateuszanella.

I think this will help so much.

[guilherme-luiz-cella]

このプルリクエストはとても良いです。