Add missing pragma once to compoundfilereader.h

thirdparty/compoundfilereader/README.txt

@@ -2,3 +2,4 @@ This directory contains the microsoft/compoundfilereader project from https://gi
 
 They are licensed under MIT, with the license text in this directory.
 
+NOTE: These files have been modified from the original. Please review existing changes if updating code.

thirdparty/compoundfilereader/compoundfilereader.h

@@ -28,6 +28,8 @@
     \endcode
 */
 
+#pragma once
+
 #include <algorithm>
 #include <stdint.h>
 #include <string.h>