Allow treating TABLESAMPLE scans as parallel-safe.

This was the intention all along, but an extraneous "return;" in
set_rel_consider_parallel() caused sampled rels to never be marked
consider_parallel.

Since we don't have any partial tablesample path/plan type yet, there's
no possibility of parallelizing the sample scan itself; but this fix
allows such a scan to appear below a parallel join, for example.

src/backend/optimizer/path/allpaths.c

@@ -538,7 +538,6 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
 				if (has_parallel_hazard((Node *) rte->tablesample->args,
 										false))
 					return;
-				return;
 			}
 
 			/*