WebBrowserComponent allows events to be emitted before backend is initialised

[eyalamir]

Maybe related to this (and the fix done as a result?):

BR: WebView Freezes DAW

This bug took us a while to reproduce! If you call either evaluateJavascript or emitEventIfBrowserIsVisible before the very first page was loaded on the WebView, this would freeze the UI when loading a project in a DAW with multiple instances loaded. To reproduce: Windows only (does not happen on Mac). Build attached plugin Load an FL Studio or Cubase project that has multiple instances loaded with their window open (attaching projects for both). The UI of any instance after the first along …