Allow NULL address to be from sender

[DenisCarriere]

Any reason why NULL_ADDRESS is excluded from valid balance changes?

Some bridging token contracts or initial token minting process use NULL_ADDRESS as from sender address

Example transaction:
https://etherscan.io/tx/0xf21fc7a2ccebe5341f0e7f22a180f2f08946ce99cc3bc1e59daf97bd1c07a3af

DAI & USDS tokens
https://etherscan.io/advanced-filter?tkn=0x6b175474e89094c44da98b954eedeac495271d0f&txntype=2&fadd=0x0000000000000000000000000000000000000000

https://etherscan.io/advanced-filter?tkn=0xdC035D45d973E3EC169d2276DDab16f1e407384F&txntype=2&fadd=0x0000000000000000000000000000000000000000

substreams-erc20-balance-changes/src/maps.rs

Lines 112 to 114 in 99907f0

	if transfer.from == NULL_ADDRESS {
	continue;
	}