One more conversion to block drain

Author: linas

opencog/persist/proxy/WriteBufferProxy.cc

@@ -163,9 +163,11 @@ void WriteBufferProxy::postRemoveAtom(AtomSpace* as, const Handle& h,
 // might forget, so we do it for them.
 if (not _value_queue.is_empty())
 {
-std::pair<Handle, Handle> pr;
-while (_value_queue.try_get(pr))
-WriteThruProxy::storeValue(pr.first, pr.second);
+size_t bufsz = _value_queue.size();
+std::vector<std::pair<Handle, Handle>> vav =
+_value_queue.try_get(bufsz);
+for (const std::pair<Handle, Handle>& kvp : vav)
+WriteThruProxy::storeValue(kvp.first, kvp.second);
 
 WriteThruProxy::barrier();
 }