Fixes bug in transaction state wrt indexes

When an index had been added to a transaction, for a particular label and property,
and the store already had a committed index for that particular label but a
different property, and you tried to look up that index, e.g. to examine its state,
then we did not properly filter out the uncommitted index when we applied the
state of the transaction to the lookup results.

This fixes #2279
Merge pull request #2374 from chrisvest/2.0-index-lookup-tx-state

Fixes bug in transaction state wrt indexes