Possible missing length check when reading a key signature meta message

[KNSN92]

Hello! I'm using this crate in one of my projects, and it has been very useful. However, I think I may have found a bug.

I tried to read some MIDI files with this crate, but parsing stopped before the end of the track. After investigating event.rs, I noticed that there does not seem to be a length check when reading a key signature meta message.

Because of this, if a MIDI file contains an invalid key signature meta message with insufficient data length, parsing stops immediately when that meta event is read. When the strict feature is enabled, it returns an error like this:

malformed midi: malformed event
  caused by: invalid midi: failed to parse event
  caused by: invalid midi: failed to read meta event
  caused by: invalid midi: failed to read the expected integer

Is this intentional behavior, or could this be a missing check?

Source:

midly/src/event.rs

Lines 575 to 577 in 0f652b5

	0x59 => {
	MetaMessage::KeySignature(u8::read(&mut data)? as i8, u8::read(&mut data)? != 0)
	}

I think it could be fixed with something like this:

0x59 if data.len() >= 2 => {
    MetaMessage::KeySignature(u8::read(&mut data)? as i8, u8::read(&mut data)? != 0)
}

After applying this change locally, I was able to process the MIDI files properly.

Sorry if my English is awkward.