ensure the max_fee_per_gas and max_priority_fee_per_gas of each UserOperation is large enough before generating bundle transaction.

[robinsdan]

This transaction contains a UO with max_fee_per_gas and max_priority_fee_per_gas be 0, and the bundler accept and submited it to the network.
https://testnet.bscscan.com/tx/0x2408177532131817065f142bc5033374c1b3fac8d057c7de4b0762473bd90272