message: Update fuzzer script with upper size bound
diff: extern crate image;
  fuzz_target!(|data: &[u8]| {
  - let _ = image::load_from_memory_with_format(data, image::ImageFormat::Tga);
  + let _ = decode(data);
  });
  +
  +fn decode(data: &[u8]) -> Result<(), image::ImageError> {
  + use image::ImageDecoder;
  + let decoder = image::codecs::tga::TgaDecoder::new(std::io::Cursor::new(data))?;
  + if decoder.total_bytes() > 4_000_000 {
  + return Ok(());
  + }
  + let mut buffer = vec![0; decoder.total_bytes() as usize];
  + decoder.read_image(&mut buffer)?;
  + Ok(())
  +}
  