This closes qax-os#2167, count characters as single runes in characters length limitation checking

Author: xuri

cell.go

@@ -1211,7 +1211,7 @@ func setRichText(runs []RichTextRun) ([]xlsxR, error) {
 		totalCellChars int
 	)
 	for _, textRun := range runs {
-		totalCellChars += len(textRun.Text)
+		totalCellChars += utf8.RuneCountInString(textRun.Text)
 		if totalCellChars > TotalCellChars {
 			return textRuns, ErrCellCharsLength
 		}

cell_test.go

@@ -1011,6 +1011,7 @@ func TestSetCellRichText(t *testing.T) {
 	}
 	assert.NoError(t, f.SetCellRichText("Sheet1", "A1", richTextRun))
 	assert.NoError(t, f.SetCellRichText("Sheet1", "A2", richTextRun))
+	assert.NoError(t, f.SetCellRichText("Sheet1", "A3", []RichTextRun{{Text: strings.Repeat("\u4e00", TotalCellChars)}}))
 	style, err := f.NewStyle(&Style{
 		Alignment: &Alignment{
 			WrapText: true,

vml.go

@@ -19,6 +19,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 )
 
 // FormControlType is the type of supported form controls.
@@ -285,20 +286,20 @@ func (f *File) addComment(commentsXML string, opts vmlOptions) error {
 		Text:     xlsxText{R: []xlsxR{}},
 	}
 	if opts.Comment.Text != "" {
-		if len(opts.Comment.Text) > TotalCellChars {
-			opts.Comment.Text = opts.Comment.Text[:TotalCellChars]
+		if utf8.RuneCountInString(opts.Comment.Text) > TotalCellChars {
+			opts.Comment.Text = string([]rune(opts.Comment.Text)[:TotalCellChars])
 		}
 		cmt.Text.T = stringPtr(opts.Comment.Text)
-		chars += len(opts.Comment.Text)
+		chars += utf8.RuneCountInString(opts.Comment.Text)
 	}
 	for _, run := range opts.Comment.Paragraph {
 		if chars == TotalCellChars {
 			break
 		}
-		if chars+len(run.Text) > TotalCellChars {
-			run.Text = run.Text[:TotalCellChars-chars]
+		if chars+utf8.RuneCountInString(run.Text) > TotalCellChars {
+			run.Text = string([]rune(run.Text)[:TotalCellChars-chars])
 		}
-		chars += len(run.Text)
+		chars += utf8.RuneCountInString(run.Text)
 		r := xlsxR{
 			RPr: &xlsxRPr{
 				Sz: &attrValFloat{Val: float64Ptr(9)},