HPCC-8908 - Std distributor not reset in child query, lost recs

The standard distributor (as opposed to the pull distributor) was
not being fully reset when restarted - which effects distributors
in child queries, e.g. in a LOOP or GRAPH.
As a consequence, after the 1st iteration of LOOP/GRAPH,
distributed rows were received but throw away.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>