File copy doesn't work with local files #152

I can't copy a file using web gui if the source or destination is a local path (this does not affect directory copy).
I see that the problem is using the rclone API copyfile, with local paths dstFs or srcFs parameter (for downloading or uploading respectively) is an empty string but it should be "/".
Example:
Current behavior:

{
    "_async": true,
    "srcFs": "gdrive:",
    "srcRemote": "folder/file.txt",
    "dstFs": "",
    "dstRemote": "/home/test/file.txt"
}

Correct behavior should be:

{
    "_async": true,
    "srcFs": "gdrive:",
    "srcRemote": "folder/file.txt",
    "dstFs": "/",
    "dstRemote": "/home/test/file.txt"
}