Restore missed original file from the latest version

[yurabakhtin]

What kind of change does this PR introduce? (check at least one)

• Bugfix

The PR fulfills these requirements:

• All tests are passing
• Changelog was modified

Other information:
Issue: https://github.com/humhub/humhub-internal/issues/96

[yurabakhtin]

I see the problem is that original file with name file is missed but a version file like old-123 exists, so I would suggest a solution from this PR #6483, I have done to restore the file from the latest version file old-123 if it exists

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maybe it is not good for performance to run the file_exists($originalFilePath) here https://github.com/humhub/humhub/pull/6483/files#diff-2f3a5cf58d46a6971793c97d7c4defb317661fce7c7cb141d28467442049dbf9R76 on each call the File->store->get(null)

I added the checking there because it is called here https://github.com/humhub/humhub/blob/master/protected/humhub/modules/file/actions/DownloadAction.php#L189-L194:

        if (!file_exists($this->file->store->get($this->variant))) {
            throw new HttpException(404, Yii::t('FileModule.base', 'Could not find requested file!'));
        }

I think it must be modified to if (!$this->file->store->has($this->variant)) and then we could run new StorageManager->restoreMissedOriginalFile() only inside the StorageManager->has($variant = null)
I have implemented this in next commit 2b47ac9.