shaping: tests panic when run more than once

[dominikh]

go test -count=1 ./shaping passes, but go test -count=2 ./shaping fails with

arabic:amiri regular On disk: 540 KB, additional memory: 2234 KB
latin:go regular On disk: 145 KB, additional memory: 337 KB
latin:roboto regular On disk: 164 KB, additional memory: 454 KB
arabic:noto sans arabic regular On disk: 747 KB, additional memory: 3590 KB
free serif regular On disk: 1647 KB, additional memory: 5593 KB
arabic:amiri regular On disk: 540 KB, additional memory: 2217 KB
latin:go regular On disk: 145 KB, additional memory: 337 KB
latin:roboto regular On disk: 164 KB, additional memory: 454 KB
arabic:noto sans arabic regular On disk: 747 KB, additional memory: 3584 KB
free serif regular On disk: 1647 KB, additional memory: 5590 KB
--- FAIL: TestWrapLine (0.00s)
    --- FAIL: TestWrapLine/simple (0.00s)
        wrapping_test.go:924: line 1: run 0: expected 4 glyphs, got 6
        wrapping_test.go:929: expected 9, got 12
    --- FAIL: TestWrapLine/simple_in_pieces_2 (0.00s)
        wrapping_test.go:924: line 1: run 1: expected 3 glyphs, got 5
        wrapping_test.go:929: expected 9, got 12
    --- FAIL: TestWrapLine/simple_fast-path (0.00s)
        wrapping_test.go:929: expected 15, got 14
--- FAIL: TestLineWrap (0.00s)
    --- FAIL: TestLineWrap/all_one_line (0.00s)
        wrapping_test.go:1526: line 0: expected shaping.Range{Offset:0, Count:15} offsets, got shaping.Range{Offset:0, Count:14}
        wrapping_test.go:1536: line 0: expected: shaping.Output{Advance:8320, Size:0, Glyphs:[]shaping.Glyph(nil), LineBounds:shaping.Bounds{Ascent:640, Descent:320, Gap:0}, GlyphBounds:shaping.Bounds{Ascent:640, Descent:0, Gap:0}, Direction:0x0, Runes:shaping.Range{Offset:0, Count:15}, Face:(*font.Face)(nil)}, got shaping.Output{Advance:8320, Size:0, Glyphs:[]shaping.Glyph(nil), LineBounds:shaping.Bounds{Ascent:640, Descent:320, Gap:0}, GlyphBounds:shaping.Bounds{Ascent:640, Descent:0, Gap:0}, Direction:0x0, Runes:shaping.Range{Offset:0, Count:14}, Face:(*font.Face)(nil)}
    --- FAIL: TestLineWrap/line_break_on_last_word (0.00s)
panic: runtime error: index out of range [0] with length 0 [recovered]
	panic: runtime error: index out of range [0] with length 0

goroutine 762 [running]:
testing.tRunner.func1.2({0x716020, 0xc00038c5d0})
	/home/dominikh/prj/go/src/testing/testing.go:1631 +0x24a
testing.tRunner.func1()
	/home/dominikh/prj/go/src/testing/testing.go:1634 +0x377
panic({0x716020?, 0xc00038c5d0?})
	/home/dominikh/prj/go/src/runtime/panic.go:770 +0x132
github.com/go-text/typesetting/shaping.inclusiveGlyphRange(...)
	/home/dominikh/prj/typesetting/shaping/wrapping.go:212
github.com/go-text/typesetting/shaping.cutRun({0x0, 0x0, {0x0, 0x0, 0x0}, {0x0, 0x0, 0x0}, {0x0, 0x0, ...}, ...}, ...)
	/home/dominikh/prj/typesetting/shaping/wrapping.go:239 +0x27b
github.com/go-text/typesetting/shaping.(*LineWrapper).processBreakOption(0xc005806b60, {0x4?}, {0x0?, 0x78?, 0x78?})
	/home/dominikh/prj/typesetting/shaping/wrapping.go:1095 +0x31e
github.com/go-text/typesetting/shaping.(*LineWrapper).wrapNextLine(0xc005806b60, {0x0?, 0xd?, 0x10?})
	/home/dominikh/prj/typesetting/shaping/wrapping.go:963 +0x13b
github.com/go-text/typesetting/shaping.(*LineWrapper).WrapNextLine(0xc005806b60, 0x78)
	/home/dominikh/prj/typesetting/shaping/wrapping.go:934 +0x7a5
github.com/go-text/typesetting/shaping.(*LineWrapper).WrapParagraph(0xc005806b60, {0x0, {0x0, 0x0, {0x0, 0x0, 0x0}, {0x0, 0x0, 0x0}, ...}, ...}, ...)
	/home/dominikh/prj/typesetting/shaping/wrapping.go:775 +0x4b8
github.com/go-text/typesetting/shaping.TestLineWrap.func1(0xc0058069c0)
	/home/dominikh/prj/typesetting/shaping/wrapping_test.go:1496 +0x117
testing.tRunner(0xc0058069c0, 0xc00574ef90)
	/home/dominikh/prj/go/src/testing/testing.go:1689 +0xfb
created by testing.(*T).Run in goroutine 755
	/home/dominikh/prj/go/src/testing/testing.go:1742 +0x390
FAIL	github.com/go-text/typesetting/shaping	0.294s
FAIL