Hi Josh,
The KalturaFlavorAsset has a member called size, you can check the $flavor_asset->size for the flavour asset that has the isOrginal set to 1.
However, I wouldn't recommend that. Checking sizes really does not ensure that the file was correctly uploaded, two files can have the exact same size and be different. This is why checksums are typically used. Unfortunately, we do not keep a checksum on the assetFlavor object.
However, just checking size IMHO is not useful. That said, if an entry managed to become ready [status == 2] it is likely that no data corruption occurred.