Projects without a public directory or explicitly configured output directory fail with globbing error

[danswick]

After the update to the latest version of webpack, it looks like some of the file copying logic has broken for projects without explicitly configured output directories. Building fails with the error:

ERROR: Cannot glob `**/*`: ENOENT: no such file or directory, stat '/myProject/public'

cc @tristen

[samanpwbb]

I was able to circumvent this by creating a public directory and putting an empty file in it, but this appears to be a straightforward bug.