[stable28] fix: don't return null for SharedStorage::getWrapperStorage with share recursion

[backportbot]

Backport of #44132

Warning, This backport's changes differ from the original and might be incomplete ⚠️

Todo

• Review and resolve any conflicts
• Amend HEAD commit to remove the line stating to skip CI

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[come-nc]

@icewind1991 Have you managed to run into this code path? I do not understand in which case can initialized be false and storage null at the same time.

[icewind1991]

@icewind1991 Have you managed to run into this code path? I do not understand in which case can initialized be false and storage null at the same time.

The process of getting the share source could lead to it recursing into the function if there (somehow) is a recursive share.

This shouldn't happen but when it does this PR improves the error behavior

[come-nc]

Oh, thank you, I think I get it now.

My first thought was moving $this->initialized = true to the end but I think it would make the recursion infinite loop actually…

[come-nc]

Suggested change

	if (!$this->storage) {
	// marked as initialized but no storage set
	// this is probably because some code path has caused recursion during the share setup
	// we setup a "failed storage" so `getWrapperStorage` doesn't return null.
	// If the share setup completes after this the "failed storage" will be overwritten by the correct one
	$this->logger->warning('Possible share setup recursion detected');
	$this->storage = new FailedStorage(['exception' => new \Exception('Possible share setup recursion detected')]);
	$this->cache = new FailedCache();
	$this->rootPath = '';
	}
	if (!$this->storage) {
	// marked as initialized but no storage set
	// this is probably because some code path has caused recursion during the share setup
	// we setup a "failed storage" so `getWrapperStorage` doesn't return null.
	// If the share setup completes after this the "failed storage" will be overwritten by the correct one
	throw new \Exception('Possible share setup recursion detected')]);
	}

This should work then, and it would be caught by the try/catch below?
Not sure if it’s cleaner because it would mean the function is now throwing.

[Altahrim]

There is a conflict on this one