Fix lineWidth object bug with fillColor: null

[mmghv]

Fixes #1001

Refs : #730, #961, #978

fillColor: null caused cells to have full borders even when lineWidth is an object with partial borders.

This is caused by calling rect() to draw the background with null as fillStyle when fillColor is null :

jsPDF-AutoTable/src/tableDrawer.ts

Lines 409 to 410 in 4c04f6a

	const fillStyle = getFillStyle(0, fillColor)
	doc.rect(cell.x, cursor.y, cell.width, cell.height, fillStyle)

Reproduce code

doc.autoTable({
  head: [['Name', 'Email', 'Country']],
  body: [
    ['David', 'david@example.com', 'Sweden'],
    ['Castille', 'castille@example.com', 'Spain'],
  ],
  theme: 'plain',
  styles: {
    // fillColor: null,
    lineColor: 0,
    lineWidth: {top: 0, bottom: 0.3, right: 0, left: 0},
  },
})

Before

After

[mmghv]

I've excluded null from being used as fillStyle with rect() which is intended to postpone setting the style when drawing multiple shapes at once, this was first introduced in this PR. this shouldn't be used as it could lead to bugs like this when misused.

[simonbengtsson]

Awesome! Tagging @MikeDabrowski in case he wants to review as well.

[MikeDabrowski]

Yep, brilliant! Thx for the fix and tagging.
I tested it on my project and had no regressions