Fix renderer getting confused by zero-length marked ranges
Fix renderer getting confused by zero-length marked ranges

Issue #313

kiejo/prosemirror,salzhrani/prosemirror,tzuhsiulin/prosemirror,tzuhsiulin/prosemirror,salzhrani/prosemirror,kiejo/prosemirror,adrianheine/prosemirror,kiejo/prosemirror,adrianheine/prosemirror,adrianheine/prosemirror,tzuhsiulin/prosemirror,salzhrani/prosemirror