LibGfx/JBIG2: Move SegmentData down a bit

Symbol segments will store decoded symbols, and for that SegmentData
needs to come after BitBuffer.

No behavior change.

Userland/Libraries/LibGfx/ImageFormats/JBIG2Loader.cpp

@@ -345,11 +345,6 @@ struct SegmentHeader {
     Optional<u32> data_length;
 };
 
-struct SegmentData {
-    SegmentHeader header;
-    ReadonlyBytes data;
-};
-
 class BitBuffer {
 public:
     static ErrorOr<NonnullOwnPtr<BitBuffer>> create(size_t width, size_t height);
@@ -434,6 +429,11 @@ BitBuffer::BitBuffer(ByteBuffer bits, size_t width, size_t height, size_t pitch)
 {
 }
 
+struct SegmentData {
+    SegmentHeader header;
+    ReadonlyBytes data;
+};
+
 // 7.4.8.5 Page segment flags
 enum class CombinationOperator {
     Or = 0,