Guard ProcessPacket against short/malformed UDP packets

[Copilot]

ProcessPacket accessed fixed byte offsets 0–17 and called Buffer.BlockCopy from offset 18 without validating data.Length, causing IndexOutOfRangeException or ArgumentException on any short or malformed UDP packet.

Changes

• Minimum header length check — if (data.Length < 18) return; added immediately after the null guard, before any index access
• Payload bounds check — if (data.Length < 18 + length) return; added after extracting length, preventing BlockCopy from reading past the buffer end
• Tightened length validation — length < 0 || length > 512 to be explicit about both bounds

if (data == null) return;
if (data.Length < 18) return;           // guards all fixed-offset reads (bytes 0–17)

// ... header/opcode validation ...

int length = (data[16] << 8) | data[17];
if (length < 0 || length > 512) return;
if (data.Length < 18 + length) return;  // guards BlockCopy

Buffer.BlockCopy(data, 18, dmxData, 0, length);

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[otoyuzu705]

@copilot
コメントは日本語でして

[Copilot]

@copilot
コメントは日本語でして

了解しました。今後のコメントは日本語で記載します。なお、今回追加したコードコメントはすでに日本語で記載しています（例：// パケット長の最低限チェック（ヘッダー18バイト以上必要）、// DMXデータ領域の長さチェック）。

[otoyuzu705]

LGTM