Fix Identify returning incorrect frame count for animated PNGs#3101
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The Identify method had two bugs when processing fdAT (FrameData) chunks: 1. A spurious Skip(4) before SkipChunkDataAndCrc caused the stream to be misaligned by 4 bytes, since chunk.Length already includes the 4-byte sequence number. 2. Unlike Decode, which consumes all fdAT chunks for a frame in one shot via ReadScanlines + ReadNextFrameDataChunk, Identify processed them individually, calling InitializeFrameMetadata for each chunk and inflating the frame count. The fix removes the extra Skip(4) and adds SkipRemainingFrameDataChunks to consume all continuation fdAT chunks for a frame, mirroring how ReadNextFrameDataChunk works during decoding.
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The Identify method had two bugs when processing fdAT (FrameData) chunks:
A spurious Skip(4) before SkipChunkDataAndCrc caused the stream to be misaligned by 4 bytes, since chunk.Length already includes the 4-byte sequence number.
Unlike Decode, which consumes all fdAT chunks for a frame in one shot via ReadScanlines + ReadNextFrameDataChunk, Identify processed them individually, calling InitializeFrameMetadata for each chunk and inflating the frame count.
The fix removes the extra Skip(4) and adds SkipRemainingFrameDataChunks to consume all continuation fdAT chunks for a frame, mirroring how ReadNextFrameDataChunk works during decoding.
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