Fix (unreported) wrong size of UserPreferences' dupflag parameter.

Adding volume obdata option to `eDupli_ID_Flags` enum made it go beyond
the 16 bits of a short... Also, enums should typically be stored in
unsigned integers.

source/blender/makesdna/DNA_userdef_types.h

@@ -633,12 +633,12 @@ typedef struct UserDef {
   /** #eUserPref_Flag. */
   int flag;
   /** #eDupli_ID_Flags. */
-  short dupflag;
+  unsigned int dupflag;
   /** #eUserPref_PrefFlag preferences for the preferences. */
   char pref_flag;
   char savetime;
   char mouse_emulate_3_button_modifier;
-  char _pad4[3];
+  char _pad4[1];
   /** FILE_MAXDIR length. */
   char tempdir[768];
   char fontdir[768];