Add a null check for ConfigDebugger creation

[acuifex]

ConfigDebugger expects to be reused, so recreating it on every run leads to a process leak (lastSeleniumBrowser and lastPuppeteerBrowser never get quit)

Something similar needs to be done for the native client, but i can't do that since i'm a linux user

Consider adding --init to the docker run command in the guide (https://github.com/puppeteer/puppeteer/issues/1825#issuecomment-792817748)

Possibly closes #213

I've also noticed memory usage increases by ~200MB when running with debug or multi run, no idea why. Seems unrelated to selenium/puppeteer and it happens with the release version too.