This patch fixes uploading for new files. Tested with Seafile 8.0 and 9.0.
It also removes some php warnings when fileapi_backend_storage_disabled is
Here's the documentation to the current web api parameters for file uploads:
To make it work we've 2 ways: request upload link with parent_dir=/full/path and upload with relative_path= or request upload link with parent_dir=/ and upload with relative_path=full/path
I opted for the 2nd version to stay in line with the old way