add Buffer::Iterator::INVALID_CODE_POINT constant

src/core/Buffer.h

@@ -14,6 +14,11 @@ public:
     class Iterator
     {
     public:
+        enum : uint32_t
+        {
+            INVALID_CODE_POINT = 0xFFFFFFFFu,
+        };
+
         Iterator(Buffer * buffer)
         {
             m_buffer = buffer;
@@ -51,7 +56,7 @@ public:
             }
             else
             {
-                return 0xFFFFFFFFu;
+                return INVALID_CODE_POINT;
             }
         }
         bool operator==(const Iterator & other) const