manual-seal with instant seal mode doesn't work with pallet-democracy or system.setCode

[xlc]

substrate/client/consensus/manual-seal/src/seal_block.rs

Lines 139 to 141 in c11a0bf

	if proposal.block.extrinsics().len() == inherents_len && !create_empty {
	return Err(Error::EmptyTransactionPool)
	}

If create_empty is false, it will refuse to create block with transaction. But pallet-democracy and some other pallets will consume all weights in on_initialize and resulting no transaction be included. This results a deadlock and break dev chain.