charSpace and maxWidth in doc.text() : charSpace > 0 and maxWidth is not respected

I have read and understood the contribution guidelines.

Basically, charSpace and maxWidth don't play nicely together.

Code tested using your live demo at http://raw.githack.com/MrRio/jsPDF/master/

The following works fine ...

var doc = new jsPDF();
doc.setFontSize(22);
doc.text("This is a title", 20, 20);

const maxWidth = 100;
const charSpace = 0;

// Drawing a box to show maxWidth clearly
doc.rect(20, 20, maxWidth, 100, 'S')

// Using 'justify' to show things clearly but also happens with 'left'
const options = {
    maxWidth: maxWidth,
    charSpace: charSpace,
    align: 'justify'
}
const str = "Mary had a little lamb she also had a duck. She put them on the mantlepiece to see if they would fall off."

doc.setFontSize(16);
doc.text(str, 20, 30, options);

However, if you change charSpace to 1 then maxWidth is not correctly applied and then text extends beyond the maxWidth boundary.

I can then adjust maxWidth to try and compensate for this, but the formula is not leaping off the page at me!

Reproduce the example in the jsPDF live demo, focusing on doc.text() with maxWidth, charSpace, and justify alignment. Trace the doc.text() implementation and verify that text with charSpace greater than zero remains within the requested maxWidth; add or update coverage if the relevant test location is identified.