[stable-34.0] fix(propagateupload): ensure file size stays the same for new uploads - #10494

It is possible that the sync engine discovers a file with a small enough
file size to use the old V1 upload propagator.  This is fine unless the file
size is still growing between discovery and propagation; should the file grow
large enough before propagation starts the propagator job may attempts to
upload the file in chunks using the old (removed with Nextcloud 30) chunking
mechanism.  Since Nextcloud 30 this no longer works as it only has support for
V2 upload chunking (PropagateUploadFileNG), resulting in broken partial
uploads while the client believes everything got uploaded.

The PropagateUploadFileCommon job already checks whether the file is
different, however relying on just the mtime is not enough for new files.

Signed-off-by: Jyrki Gadinger <[email protected]>