Prevent taglib from corrupting flac files

Prevent taglib from corrupting flac files when embedded album art exceeds 16Mb

src/TagLib/Flac/BlockHeader.cs

@@ -137,6 +137,10 @@ public BlockHeader (ByteVector data)
 		/// </param>
 		public BlockHeader (BlockType type, uint blockSize)
 		{
+			if (blockSize > 0xffffff)
+				throw new CorruptFileException (
+					"Block size too large.");
+
 			block_type    = type;
 			is_last_block = false;
 			block_size    = blockSize;
@@ -194,4 +198,4 @@ public ByteVector Render (bool isLastBlock)
 			get {return block_size;}
 		}
 	}
-}
+}