Fixed issue with prematurely exhausted iterator.

By exhausting the iterator on initialization, some queries lead to a lot
of unnecessary dbhits, e.g.
````
profile MATCH (n:topic)-[r]->(m:topic) return n,r,m limit 1;

+------------------+------+----------+-------------+----------------------+
|         Operator | Rows |   DbHits | Identifiers |                Other |
+------------------+------+----------+-------------+----------------------+
|            Slice |    1 |        0 |             |         {  AUTOINT0} |
|           Filter |    1 |        1 |             | hasLabel(m:topic(0)) |
| TraversalMatcher |    1 | 11292978 |             |              m, r, m |
+------------------+------+----------+-------------+----------------------+

Total database accesses: 11292979
````
should ideally only touch a small portion of the graph but ends up touching something like
50% instead. This fix I believe fix this.
It looks like there are no actual changes in this class. You should remove this change from the commit since this is an older maint branch and any change will make merging more difficult.