text: fix additional truncated newline bug

This commit fixes another rune accounting bug that the fuzzer discovered. If we
shaped a space in order to acquire line metrics, but the space itself was truncated,
we would reset the truncated count to zero. This had the side effect of lying to
later logic about whether the truncator run was present at the end of the shaped
text.

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

text/gotext.go

@@ -528,6 +528,7 @@ func (s *shaperImpl) LayoutRunes(params Parameters, txt []rune) document {
 	if hasNewline {
 		txt = txt[:len(txt)-1]
 	}
+	truncatedNewline := false
 	if hasNewline && len(txt) == 0 {
 		// If we only have a newline, shape a space to get line metrics.
 		ls, truncated = s.shapeAndWrapText(params, []rune{' '})
@@ -535,6 +536,7 @@ func (s *shaperImpl) LayoutRunes(params Parameters, txt []rune) document {
 			// Our space was truncated. Since our space didn't exist in any meaningful
 			// capacity, ensure the truncated count is zeroed out.
 			truncated = 0
+			truncatedNewline = true
 		} else {
 			// We shaped a space to get proper line metrics, but we need to drop
 			// the rune/glyph info since it isn't actually part of the text.
@@ -546,7 +548,7 @@ func (s *shaperImpl) LayoutRunes(params Parameters, txt []rune) document {
 		ls, truncated = s.shapeAndWrapText(params, replaceControlCharacters(txt))
 	}
 
-	didTruncate := truncated > 0 || (params.forceTruncate && params.MaxLines == len(ls))
+	didTruncate := truncated > 0 || truncatedNewline || (params.forceTruncate && params.MaxLines == len(ls))
 
 	if didTruncate && hasNewline {
 		// We've truncated the newline, since it was at the end and we've truncated some amount of runes