[bug] Fix string size in UDF2.5 FID

File or directory names in Field Identifier Descriptors are not fixed size, therefore the string size byte does not need to be added at the end of the string.
This is fixed by omitting one byte before padding with zero bytes.

tsMuxer/iso_writer.cpp

@@ -279,6 +279,7 @@ void ByteFileWriter::writeDString(const std::string& value, int len) { writeDStr
 
 void ByteFileWriter::doPadding(int padSize)
 {
+    m_curpos--;
     int rest = (m_curPos - m_buffer) % padSize;
     if (rest)
     {