Fix potential negative write pool

code/go/0chain.net/smartcontract/storagesc/writepool.go

@@ -2,6 +2,7 @@ package storagesc
 
 import (
 	"encoding/json"
+	"fmt"
 
 	cstate "0chain.net/chaincore/chain/state"
 	"0chain.net/chaincore/state"
@@ -80,21 +81,27 @@ func (ssc *StorageSmartContract) writePoolLock(
 	}
 
 	if allocation.Finalized || allocation.Canceled {
-		return "", common.NewError("write_pool_unlock_failed",
+		return "", common.NewError("write_pool_lock_failed",
 			"can't lock tokens with a finalized or cancelled allocation")
 
 	}
 
 	allocation.WritePool, err = currency.AddCoin(allocation.WritePool, txn.Value)
-	i, _ := txn.Value.Int64()
+	if err != nil {
+		return "", common.NewError("write_pool_lock_failed", fmt.Sprintf("write pool token overflow: %v", err))
+	}
+
+	i, err := txn.Value.Int64()
+	if err != nil {
+		return "", common.NewError("write_pool_lock_failed", fmt.Sprintf("invalid lock value: %v", err))
+	}
+
 	balances.EmitEvent(event.TypeStats, event.TagLockWritePool, allocation.ID, event.WritePoolLock{
 		Client:       txn.ClientID,
 		AllocationId: allocation.ID,
 		Amount:       i,
 	})
-	if err != nil {
-		return "", common.NewError("write_pool_unlock_failed", err.Error())
-	}
+
 	if err := allocation.saveUpdatedStakes(balances); err != nil {
 		return "", common.NewError("write_pool_lock_failed", err.Error())
 	}