fix oneline overflow (copy from pr#226)

[zodimo]

I have discovered this bug when updating go-text/typesetting to v0.3.3 and the gioui/widget.Editor SingleLine=true stopped working and text was displayed vertical one character per line. I have traced it to widget/text.go line 246-254.

	maxWidth := gtx.Constraints.Max.X
	if e.SingleLine {
		maxWidth = math.MaxInt
	}
	minWidth := gtx.Constraints.Min.X
	if maxWidth != e.params.MaxWidth {
		e.params.MaxWidth = maxWidth
		e.invalidate()
	}

Which caused and overflow in text/gotext.go line 514.

	return s.wrapper.WrapParagraph(wc, params.MaxWidth, txt, shaping.NewSliceIterator(s.shapeText(params.PxPerEm, params.Locale, txt)))

which progressed to shaping/wrapping.go from github.com/go-text/typesetting v 0.3.3, where the overflow occurs. fixed.I(maxWidth) -> -64 when maxWidth is math.MaxInt

func (l *LineWrapper) WrapParagraph(config WrapConfig, maxWidth int, paragraph []rune, runs RunIterator) (_ []Line, truncated int) {
	return l.WrapParagraphF(config, fixed.I(maxWidth), paragraph, runs)
}

The error before the fix was applied.

--- FAIL: TestWrapping_oneLine_overflow_bug (0.00s)
    wrapping_test.go:3614: expected one line, got 2
    wrapping_test.go:3620: expected no line, got 2

I have created a safety check for the overflow and created a test to verify

[zodimo]

The checks are still waiting. I dont know how to fix this.