avoid linux compile issue

/home/runner/work/NppFTP/NppFTP/src/Windows/Treeview.cpp:215:45: error: ‘pow’ was not declared in this scope
  215 |                                 if (fsize > pow(1024, i)) {
      |                                             ^~~

Author: chcg

src/Windows/Treeview.cpp

@@ -19,6 +19,7 @@
 #include "StdInc.h"
 #include "Treeview.h"
 #include "ut_strop.h"
+#include <math.h>
 
 /* Tree view extended styles */
 #if 1