Static folder doesn't always copy all files if root destination folder does not yet exist

[angelsix]

Give a dna.config file similar to:

{
    "outputPath": "../WebRoot",
    "staticFolders": 
    [ 
        { "source": "Assets", "destination": "../WebRoot/Assets" },
        { "source": "Assets", "destination": "../ServerRoot/wwwroot/Assets" } 
    ]
}

If ../WebRoot does not exist, on the first run of dnaweb, only some of the files copy (say 14 of 44 files). Running another generate command, or creating the WebRoot folder initially before running dnaweb solves the problem