Overlay: overwriting the API endpoint with setAPIUrl does not work in JS

[mattab]

Reported by Michal:

I checked this setApiUrl method for js tracker and there seems to be problem with order of executing fuctions
for some reason trackPageView gets triggered before setAPIUrl and therefore overlay isn't initialized with proper URL
if I put 'trackPageView' in setTimeout statement, then it works ok but I believe it's not a proper solution to this

[mattab]

In c27698f: Fixes #4856 Make sure setAPIUrl, when called, is executed before any other request is sent.