wallet2: speedup large tx construction: reserve vector memory

2.8 seconds -> 2.6 seconds on a test case

src/wallet/wallet2.cpp

@@ -8583,6 +8583,7 @@ void wallet2::get_outs(std::vector<std::vector<tools::wallet2::get_outs_entry>>
     cryptonote::COMMAND_RPC_GET_OUTPUT_HISTOGRAM::request req_t = AUTO_VAL_INIT(req_t);
     cryptonote::COMMAND_RPC_GET_OUTPUT_HISTOGRAM::response resp_t = AUTO_VAL_INIT(resp_t);
     // request histogram for all outputs, except 0 if we have the rct distribution
+    req_t.amounts.reserve(selected_transfers.size());
     for(size_t idx: selected_transfers)
       if (!m_transfers[idx].is_rct() || !has_rct_distribution)
         req_t.amounts.push_back(m_transfers[idx].is_rct() ? 0 : m_transfers[idx].amount());
@@ -8610,6 +8611,7 @@ void wallet2::get_outs(std::vector<std::vector<tools::wallet2::get_outs_entry>>
     {
       cryptonote::COMMAND_RPC_GET_OUTPUT_DISTRIBUTION::request req_t = AUTO_VAL_INIT(req_t);
       cryptonote::COMMAND_RPC_GET_OUTPUT_DISTRIBUTION::response resp_t = AUTO_VAL_INIT(resp_t);
+      req_t.amounts.reserve(req_t.amounts.size() + selected_transfers.size());
       for(size_t idx: selected_transfers)
         req_t.amounts.push_back(m_transfers[idx].is_rct() ? 0 : m_transfers[idx].amount());
       std::sort(req_t.amounts.begin(), req_t.amounts.end());
@@ -8688,6 +8690,8 @@ void wallet2::get_outs(std::vector<std::vector<tools::wallet2::get_outs_entry>>
       gamma.reset(new gamma_picker(rct_offsets));
 
     size_t num_selected_transfers = 0;
+    req.outputs.reserve(selected_transfers.size() * (base_requested_outputs_count + CRYPTONOTE_MINED_MONEY_UNLOCK_WINDOW));
+    daemon_resp.outs.reserve(selected_transfers.size() * (base_requested_outputs_count + CRYPTONOTE_MINED_MONEY_UNLOCK_WINDOW));
     for(size_t idx: selected_transfers)
     {
       ++num_selected_transfers;