Fix potential race with parallel processing of txes/signatures/blocks

src/cryptonote_core/blockchain.cpp

@@ -2159,6 +2159,7 @@ bool Blockchain::check_tx_inputs(const transaction& tx, tx_verification_context
         if(ioservice_active) \
         { \
             work.reset(); \
+            while (!ioservice.stopped()) ioservice.poll(); \
             threadpool.join_all(); \
             ioservice.stop(); \
             ioservice_active = false; \

src/wallet/wallet2.cpp

@@ -73,6 +73,7 @@ using namespace cryptonote;
 #define KILL_IOSERVICE()  \
     do { \
       work.reset(); \
+      while (!ioservice.stopped()) ioservice.poll(); \
       threadpool.join_all(); \
       ioservice.stop(); \
     } while(0)