/// \brief Returns offset (since the beginning of the file, including
/// the File Preamble, if any) of the value of the current Dicom HeaderEntry
/// \warning offset of the *value*, not of the Dicom Header Entry
/// \brief Returns offset (since the beginning of the file, including
/// the File Preamble, if any) of the value of the current Dicom HeaderEntry
/// \warning offset of the *value*, not of the Dicom Header Entry