add c_oSerCellTypes::ValueText for cell value; Read1 error with empty length

XlsxSerializerCom/Common/BinReaderWriterDefines.h

@@ -298,7 +298,8 @@ namespace BinXlsxRW
 		Type = 2,
 		Value = 3,
 		Formula = 4,
-		RefRowCol = 5
+		RefRowCol = 5,
+		ValueText = 6
 	};}
 	namespace c_oSerFormulaTypes{enum c_oSerFormulaTypes
 	{

XlsxSerializerCom/Writer/BinaryCommonReader.h

@@ -79,7 +79,7 @@ namespace BinXlsxRW {
 					return c_oSerConstants::ReadOk;
 				} 
 				res = (((CallbackType*)poFuncObj)->*fReadFunction)(type, length, arg);
-                if(res == c_oSerConstants::ReadUnknown && length > 0)
+				if(res == c_oSerConstants::ReadUnknown)
 				{
 					m_oBufferedStream.GetPointer(length);
 					res = c_oSerConstants::ReadOk;

XlsxSerializerCom/Writer/BinaryReader.h

@@ -3555,6 +3555,11 @@ namespace BinXlsxRW {
 				pCell->m_oValue.Init();
 				pCell->m_oValue->m_sText.append(OOX::Spreadsheet::SpreadsheetCommon::WriteDouble(dValue));
 			}
+			else if(c_oSerCellTypes::ValueText == type)
+			{
+				pCell->m_oValue.Init();
+				pCell->m_oValue->m_sText.append(m_oBufferedStream.GetString4(length));
+			}
 			else
 				res = c_oSerConstants::ReadUnknown;
 			return res;