Assigning something to `process.env.profile`, Node stringifies the value. This
means that assigning `undefined` to an environment variable in Node will result
in it holding the string `undefined`.
This means, for example, that `module.exports.FFPROBE_PATH || 'ffprobe'` in
`server/libs/nodeFfprobe/index.js` will actually result in the string
`undefined`.
This patch fixes several such assignments in the `index.js`, potentially
causing problems in the development mode.