Only emit "load" when sync is set to true

[SamyPesse]

This PR fixes an issue when we use doc.emit('sync', [false]), at the moment, it'll emit load and change isLoaded to true.

In our case, we call doc.emit('sync', [false]) when our socket connection is dropped; and sometimes it can happen before the first time we called doc.emit('sync', [true]).

The alternative to this PR is to change the logic of the sync event to not accept an argument and to behave like the load event where calling it always set the state to true.

The workaround at the moment is to make sure to wrap doc.emit('sync', [false]) with if (doc.isSynced) { }.

[dmonad]

Sorry for the long wait! I merged it and will make a release soon!