Guarded allocator: Override placement new operator

Allows to in-place construct objects which are using guarded allocator.

intern/guardedalloc/MEM_guardedalloc.h

@@ -239,6 +239,10 @@ void MEM_use_guarded_allocator(void);
     { \
       if (mem) \
         MEM_freeN(mem); \
+    } \
+    void *operator new(size_t /*count*/, void *ptr) \
+    { \
+      return ptr; \
     }
 
 /* Needed when type includes a namespace, then the namespace should not be