to prevent excel file corruption, Set non-numeric data as a string ce…

…ll instead of a numeric type cell.

Note: if not, bad numeric type cell causes "(filename.xlsx)の一部の内容に問題が見つかりました。可能な限り内容を回復しますか？" in the Japanese version of Excel.
(English version perhaps "Excel found unreadable contents in (filename.xlsx). Do you want to recover the contents of this workbook?")

xlsxwriter.class.php

@@ -369,7 +369,11 @@ protected function writeCell(XLSXWriter_BuffererWriter &$file, $row_number, $col
 		} elseif ($num_format_type=='n_datetime') {
 			$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="n"><v>'.self::convert_date_time($value).'</v></c>');
 		} elseif ($num_format_type=='n_numeric') {
-			$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="n"><v>'.self::xmlspecialchars($value).'</v></c>');//int,float,currency
+			if (!is_string($value) || $value=='0' || ($value[0]!='0' && ctype_digit($value)) || preg_match("/^\-?(0|[1-9][0-9]*)?(\.[0-9]+)?$/", $value)){
+				$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="n"><v>'.self::xmlspecialchars($value).'</v></c>');//int,float,currency
+			} else { //not numeric, treat it as string
+				$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="inlineStr"><is><t>'.self::xmlspecialchars($value).'</t></is></c>');
+			}
 		} elseif ($num_format_type=='n_string') {
 			$file->write('<c r="'.$cell_name.'" s="'.$cell_style_idx.'" t="inlineStr"><is><t>'.self::xmlspecialchars($value).'</t></is></c>');
 		} elseif ($num_format_type=='n_auto' || 1) { //auto-detect unknown column types