Returns a floating-point value between 0.0 and 1.0, indicating the progress of downloading body data from the server. (Read Only)
Note: This property only works if the server’s response contains a Content-Length header and the UnityWebRequest has a DownloadHandler attached to the downloadHandler property.
If the UnityWebRequest is complete (either a success or a system error), this property will always return 1. If the UnityWebRequest is still communicating with the remote server, and downloadHandler is
null, this property will return 0.5. If Send has not yet been called, this property will return -1.