does not load project in "nimn" format

[alex89607]

Describe the bug
does not load project in "nimn" format with polygons

To Reproduce
it can be reproduced at online(https://imglab.in/#) and local(http://localhost/imglab) version at the same time:

2. open picture, draw one polygon.
3. save project at NIMN format ("test.nimn")
4. reload page and open same picture
5. select picture at bottom
6. open project("test.nimn")
7. click on picture at bottom - see nothing (lack of polygon)

Console Errors
None

**Device detail

1. windows 10/64.
   Firefox 75.0 (64-битный)
   Chrome Версия 81.0.4044.92 (Официальная сборка), (64 бит)

**Additional information
JSON save\load works well

[franz101]

Having another bug when opening:
TypeError: point.map is not a function. (In 'point.map(val => val * scale)', 'point.map' is undefined)