TRO opcode does not revert when amount=0

[Dentosal]

The specification states that TRO should panic if the amount ($rC) is zero but the implementation does not perform this validation. TR performs this validation.

fuel-vm/fuel-vm/src/interpreter/contract.rs

Lines 290 to 367 in ae96189

	pub(crate) fn transfer_output(
	self,
	a: Word,
	b: Word,
	c: Word,
	d: Word,
	) -> Result<(), RuntimeError>
	where
	Tx: ExecutableTransaction,
	S: ContractsAssetsStorage,
	<S as StorageInspect<ContractsAssets>>::Error: Into<std::io::Error>,
	{
	let ax = a
	.checked_add(ContractId::LEN as Word)
	.ok_or(PanicReason::ArithmeticOverflow)?;
	let dx = d
	.checked_add(AssetId::LEN as Word)
	.ok_or(PanicReason::ArithmeticOverflow)?;
	// if above usize::MAX then it cannot be safely cast to usize,
	// check the tighter bound between VM_MAX_RAM and usize::MAX
	if ax > MIN_VM_MAX_RAM_USIZE_MAX || dx > MIN_VM_MAX_RAM_USIZE_MAX {
	return Err(PanicReason::MemoryOverflow.into())
	}
	let out_idx = b as usize;
	let to = Address::try_from(&self.memory[a as usize..ax as usize])
	.expect("Unreachable! Checked memory range");
	let asset_id = AssetId::try_from(&self.memory[d as usize..dx as usize])
	.expect("Unreachable! Checked memory range");
	let amount = c;
	let internal_context = match internal_contract(self.context, self.fp, self.memory)
	{
	// optimistically attempt to load the internal contract id
	Ok(source_contract) => Some(*source_contract),
	// revert to external context if no internal contract is set
	Err(RuntimeError::Recoverable(PanicReason::ExpectedInternalContext)) => None,
	// bubble up any other kind of errors
	Err(e) => return Err(e),
	};
	if let Some(source_contract) = internal_context {
	// debit funding source (source contract balance)
	balance_decrease(self.storage, &source_contract, &asset_id, amount)?;
	} else {
	// debit external funding source (i.e. UTXOs)
	external_asset_id_balance_sub(self.balances, self.memory, &asset_id, amount)?;
	}
	// credit variable output
	let variable = Output::variable(to, amount, asset_id);
	set_variable_output(self.tx, self.memory, self.tx_offset, out_idx, variable)?;
	let receipt = Receipt::transfer_out(
	internal_context.unwrap_or_default(),
	to,
	amount,
	asset_id,
	*self.pc,
	*self.is,
	);
	append_receipt(
	AppendReceipt {
	receipts: self.receipts,
	script: self.tx.as_script_mut(),
	tx_offset: self.tx_offset,
	memory: self.memory,
	},
	receipt,
	);
	inc_pc(self.pc)
	}
	}

Either update the specification, or add validation behavior. This should have a test case as well.