Add missing include

code/Common/StackAllocator.h

@@ -4,7 +4,6 @@ Open Asset Import Library (assimp)
 
 Copyright (c) 2006-2022, assimp team
 
-
 All rights reserved.
 
 Redistribution and use of this software in source and binary forms,
@@ -36,7 +35,6 @@ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
 ----------------------------------------------------------------------
 */
 
@@ -52,9 +50,9 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <deque>
 #include <stdint.h>
+#include <stddef.h>
 
-namespace Assimp
-{
+namespace Assimp {
 
 /** @brief A very bare-bone allocator class that is suitable when
  *      allocating many small objects, e.g. during parsing.