miner: avoid unnecessary work (#15883)

core/gaspool.go

@@ -44,6 +44,11 @@ func (gp *GasPool) SubGas(amount uint64) error {
 	return nil
 }
 
+// Gas returns the amount of gas remaining in the pool.
+func (gp *GasPool) Gas() uint64 {
+	return uint64(*gp)
+}
+
 func (gp *GasPool) String() string {
 	return fmt.Sprintf("%d", *gp)
 }