simplewallet: single out 0 amount destinations as dummy ones

Avoids surprising the user with "sending 0 to..."

src/simplewallet/simplewallet.cpp

@@ -4669,12 +4669,24 @@ bool simple_wallet::accept_loaded_tx(const std::function<size_t()> get_num_txes,
     payment_id_string = "no payment ID";
 
   std::string dest_string;
+  size_t n_dummy_outputs = 0;
   for (auto i = dests.begin(); i != dests.end(); )
   {
-    dest_string += (boost::format(tr("sending %s to %s")) % print_money(i->second.second) % i->second.first).str();
+    if (i->second.second > 0)
+    {
+      if (!dest_string.empty())
+        dest_string += ", ";
+      dest_string += (boost::format(tr("sending %s to %s")) % print_money(i->second.second) % i->second.first).str();
+    }
+    else
+      ++n_dummy_outputs;
     ++i;
-    if (i != dests.end())
+  }
+  if (n_dummy_outputs > 0)
+  {
+    if (!dest_string.empty())
       dest_string += ", ";
+    dest_string += std::to_string(n_dummy_outputs) + tr(" dummy output(s)");
   }
   if (dest_string.empty())
     dest_string = tr("with no destinations");