message: Add a sanity check to fix arithmetic overflow
diff: @@ -231,6 +231,11 @@ impl<R: Read + Seek> TGADecoder<R> {
  let other_channel_bits = if self.header.map_type != 0 {
  self.header.map_entry_size
  } else {
  + if num_alpha_bits > self.header.pixel_depth {
  + return Err(ImageError::UnsupportedError(format!("\
  + Color format not supported. Alpha bits: {}", num_alpha_bits).to_string()))
  + }
  +
  self.header.pixel_depth - num_alpha_bits
  };
  let color = self.image_type.is_color();
  