Bugfix: Don't abort upload if chunk is locked

Since 2.9 we know that we need exclusive file access to a file to properly handle it with Windows virtual files.
Therefore, we checked for the locked state before we start the upload.
Due to a bug we checked that for each file chunk, now we only check when the upload starts and when it finished completely.

https://github.com/owncloud/client/issues/9194
https://github.com/owncloud/client/pull/9264
https://github.com/owncloud/client/pull/9296
