fix problem of first payout being too large

When reward_fund_object was originally created during HF17, its last_update field was set to the time of creation. Now it is created during genesis
and as a result last_update was far into the past on first payout resulting in wrong payout values that later caused problems with replay.

Author: ABW

libraries/chain/database_hardfork.cpp

@@ -275,6 +275,7 @@ void database::apply_hardfork( uint32_t hardfork )
 
         modify( get_reward_fund(), [&]( reward_fund_object& rfo )
         {
+          rfo.access_last_update() = head_block_time();
 #ifndef IS_TEST_NET
           rfo.access_recent_claims() = HIVE_HF_17_RECENT_CLAIMS;
 #endif