fix for infinite loop on bad changeset

[dmitryuv]

In case pad state is broken, or bad changeset somehow was submitted to the store, this check is required to avoid infinite loop in the consuming code.

[marcelklehr]

Will need some testing

[dmitryuv]

@marcelklehr interested in 50% performance improvement for v8 with the changesets library? can make another pull request, but it changes a lot (mainly closures->prototype classes and removal of outdated "optimizations")

[marcelklehr]

hoh! sounds interesting, will the exposed module API change?

[JohnMcLear]

Does it break any functionality at all? So far sounds good :) thanks dmitry and in general very pleased you are finding the time and energy to contribute, we appreciate it!

[dmitryuv]

@marcelklehr no it don't, API is the same. It's just cosmetic code changes here and there, not "deep refactoring". Everything else is the same. I'll test more with real data and make pull request if everything works fine. Tests are running fine too, but i'm not sure they cover everything.

[JohnMcLear]

@marcelklehr you happy for this to be merged?

[marcelklehr]

I barely glanced at this change, it looks like it makes sense. Basic
editing seems to work. It would of course be helpful to have a test case
that fails in the old version and passes with this change.

If it works for dmitry, I guess we can just pull it.