editor.blocks.getCurrentBlockIndex gives incoherent internal value on start

- Describe a bug.
On start/load, editor.blocks.getCurrentBlockIndex() return last index of the block inserted

- Steps to reproduce:
[see example](http://sosie.sos-productions.com/editor.js/example/example-invalid-internal-blockindex.html)
Finish the demo by clicking on the button of the Truth..the saving button gives the expected behavior

- Expected behavior:
should return -1 expected as no block is selected

Screenshots:

Device, Browser, OS: FF+linux

Editor.js version: 2.1.9

Plugins you use with their versions: Independant of the plugin