text: ensure truncated consecutive newlines are handled

This commit ensures that multiple newlines in a row still produce expected
results when occuring within a truncated string. The problem was that we usually
wrap text that is truncated in a way that forces the truncator symbol to appear
at the end *unless* we know we're on the final paragraph of the input text. This
is the right behavior for text that will be displayed, but when shaping a paragraph
containing nothing but a newline, we do not want the truncator symbol in our line.
I simply had to disable the forced truncation contextually to make it work.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

text/gotext.go

@@ -530,6 +530,7 @@ func (s *shaperImpl) LayoutRunes(params Parameters, txt []rune) document {
 	}
 	truncatedNewline := false
 	if hasNewline && len(txt) == 0 {
+		params.forceTruncate = false
 		// If we only have a newline, shape a space to get line metrics.
 		ls, truncated = s.shapeAndWrapText(params, []rune{' '})
 		if truncated > 0 {

text/shaper_test.go

@@ -163,6 +163,8 @@ func TestShapingNewlineHandling(t *testing.T) {
 		{textInput: "a\nb", expectedLines: 2, expectedGlyphs: 3},
 		{textInput: "", expectedLines: 1, expectedGlyphs: 1},
 		{textInput: "\n", expectedLines: 1, expectedGlyphs: 2},
+		{textInput: "\n\n", expectedLines: 2, expectedGlyphs: 3},
+		{textInput: "\n\n\n", expectedLines: 3, expectedGlyphs: 4},
 	} {
 		t.Run(fmt.Sprintf("%q", tc.textInput), func(t *testing.T) {
 			ltrFace, _ := opentype.Parse(goregular.TTF)
@@ -497,6 +499,32 @@ func TestShapeStringRuneAccounting(t *testing.T) {
 				MaxWidth:   0,
 			},
 		},
+		{
+			name:  "double newline regression",
+			input: "\n\n",
+			params: Parameters{
+				Font:       font.Font{Typeface: "Go", Style: font.Regular, Weight: font.Normal},
+				Alignment:  Start,
+				PxPerEm:    768,
+				MaxLines:   1,
+				Truncator:  "\u200b",
+				WrapPolicy: WrapHeuristically,
+				MaxWidth:   1000,
+			},
+		},
+		{
+			name:  "triple newline regression",
+			input: "\n\n\n",
+			params: Parameters{
+				Font:       font.Font{Typeface: "Go", Style: font.Regular, Weight: font.Normal},
+				Alignment:  Start,
+				PxPerEm:    768,
+				MaxLines:   1,
+				Truncator:  "\u200b",
+				WrapPolicy: WrapHeuristically,
+				MaxWidth:   1000,
+			},
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			for _, setup := range []setup{