Typo in message for NoMoreImageData

[misos1]

There is typo in: https://github.com/image-rs/image-png/blob/master/src/decoder/stream.rs#L296 "IDAT or fDAT chunk is has not enough data for image."

[misos1]

Also this message looks strange: InvalidBitDepth(nr) => write!(fmt, "Invalid dispose operation {}.", nr) Should not it be something about invalid bit depth? There is already something about "dispose op": InvalidDisposeOp(nr) => write!(fmt, "Invalid dispose op {}.", nr)