fixed return_payment issues for N-out-TXs; fixed change_index being incorrect datatype; partial fix to asset_type RPC propagation issue

src/cryptonote_core/cryptonote_tx_utils.cpp

@@ -856,7 +856,7 @@ namespace cryptonote
     uint64_t summary_outs_money = 0;
     //fill outputs
     size_t output_index = 0;
-    size_t change_index = 0;
+    uint8_t change_index = 0;
     for(const tx_destination_entry& dst_entr: destinations)
     {
       CHECK_AND_ASSERT_MES(dst_entr.amount > 0 || tx.version > 1, false, "Destination with wrong amount: " << dst_entr.amount);