Remove an unnecessary iterator increment.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

src/wallet/walletdb.cpp

@@ -1144,7 +1144,7 @@ void ThreadFlushWalletDB(const string& strFile)
                         bitdb.CloseDb(strFile);
                         bitdb.CheckpointLSN(strFile);
 
-                        bitdb.mapFileUseCount.erase(mi++);
+                        bitdb.mapFileUseCount.erase(mi);
                         LogPrint("db", "Flushed %s %dms\n", strFile, GetTimeMillis() - nStart);
                     }
                 }