Tech debt: make rollapp.GetRevisionForHeight more robust to missing heights

[danwt]

Should return also and error or OK bool. The current method is bug prone

[mtsitrin]

can u elaborate what the possible bug is?

func (r Rollapp) GetRevisionForHeight(h uint64) Revision {
	for i := len(r.Revisions) - 1; i >= 0; i-- {
		if r.Revisions[i].StartHeight <= h {
			return r.Revisions[i]
		}
	}
	return Revision{}
}