Create a safe without funds on a private network with gasPrice null

[Sorag]

You should add the option to create a safe even without funds when the network has a gasPrice null

Describe the bug
I can't create a safe on a private network where the gasPrice is null because the account doesn't have funds (even if not needed)
It is irrelevant to test if the account have enough funds to do the Tx on a private network where the gasPrice is null

To Reproduce
Steps to reproduce the behavior:

1. Create a network with gasPrice null
2. Create a safe