fix(Point): safeguard initialization

[ShaMan123]

This PR fixes Point so that the following

new fabric.Point().scalarAdd(5)

will result in Point(5, 5) instead of Nan

[github-actions]

Code Coverage Summary

> fabric@5.1.0 coverage:report
> nyc report --reporter=lcov --reporter=text

-----------|---------|----------|---------|---------|-----------------------------------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                             
-----------|---------|----------|---------|---------|-----------------------------------------------
All files  |   83.05 |    75.99 |   85.69 |   82.78 |                                               
 fabric.js |   83.05 |    75.99 |   85.69 |   82.78 | ...,30850,30924,30935-31000,31123,31222,31458 
-----------|---------|----------|---------|---------|-----------------------------------------------

[github-actions]

Code Coverage Summary

> fabric@5.1.0 coverage:report
> nyc report --reporter=lcov --reporter=text

-----------|---------|----------|---------|---------|-----------------------------------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                             
-----------|---------|----------|---------|---------|-----------------------------------------------
All files  |   83.05 |    75.99 |   85.69 |   82.78 |                                               
 fabric.js |   83.05 |    75.99 |   85.69 |   82.78 | ...,30850,30924,30935-31000,31123,31222,31458 
-----------|---------|----------|---------|---------|-----------------------------------------------

[ShaMan123]

Alrighty.
Before merging I want to be a little cautious...
Why do you think it was written like this in the first place?

[asturur]

yes this makes sense. I would also say people have to read docs and not pass undefined in a point, but also is so little change that is fine by me