fix for 0x9fb: pool[pool_shares] was still a string, so p_join_pool() did not expect that it had to convert to a Decimal. Most likely 0x8b6 had an action that properly did Decimal conversion before p_join_pool() was triggered

Author: randomshinichi

model/parts/system_policies.py

@@ -124,7 +124,7 @@ def p_join_pool(params, step, history, current_state, action):
                                                                                                                                amount_expected,
                                                                                                                                symbol))
         pool['tokens'][symbol].balance += amount
-    pool['pool_shares'] += pool_amount_out
+    pool['pool_shares'] = Decimal(pool['pool_shares']) + pool_amount_out
 
     return pool