Avoid reading unused bytes from PNG streams (#535)

Co-authored-by: Milan Nikl <[email protected]>

Source/com/drew/imaging/png/PngChunkReader.java

@@ -69,6 +69,12 @@ public Iterable<PngChunk> extract(@NotNull final SequentialReader reader, @Nulla
         //     Miscellaneous information: bKGD, hIST, pHYs, sPLT
         //     Time information:          tIME
         //
+        // CHUNK READING
+        //
+        // Only chunk data for types specified in desiredChunkTypes is extracted.
+        // For empty chunk type list NO data is copied from source stream.
+        // For null chunk type list ALL data is copied from source stream.
+        //
 
         reader.setMotorolaByteOrder(true); // network byte order
 
@@ -93,7 +99,13 @@ public Iterable<PngChunk> extract(@NotNull final SequentialReader reader, @Nulla
 
             boolean willStoreChunk = desiredChunkTypes == null || desiredChunkTypes.contains(chunkType);
 
-            byte[] chunkData = reader.getBytes(chunkDataLength);
+            byte[] chunkData;
+            if (willStoreChunk) {
+                chunkData = reader.getBytes(chunkDataLength);
+            } else {
+                chunkData = null; // To satisfy the compiler
+                reader.skip(chunkDataLength);
+            }
 
             // Skip the CRC bytes at the end of the chunk
             // TODO consider verifying the CRC value to determine if we're processing bad data