Fix UnboundLocalError in select_coins

[kyurais]

bit/bit/transaction.py

Lines 316 to 329 in d351d1d

	while unspents:
	selected_coins.append(unspents.pop(0))
	estimated_fee = estimate_tx_fee(
	sum(u.vsize for u in selected_coins), len(selected_coins), sum(output_size), len(output_size), fee, any(u.segwit for u in selected_coins)
	)
	estimated_fee = fee if absolute_fee else estimated_fee
	remaining = sum(u.amount for u in selected_coins) - target - estimated_fee
	if remaining >= min_change and (not consolidate or len(unspents) == 0):
	break
	else:
	raise InsufficientFunds(
	'Balance {} is less than {} (including '
	'fee).'.format(sum(u.amount for u in selected_coins), target + min_change + estimated_fee)
	)

estimated_fee integer is initialized within the while block of select_coins, resulting in UnboundLocalError in the case when an empty container is provided for the unspents argument.

from bit.transaction import select_coins

# Should raise InsufficientFunds
s = select_coins(10000, 1, [42], 100, unspents=[])

UnboundLocalError: cannot access local variable 'estimated_fee' where it is not associated with a value

The PR proposes to initialize the estimated_fee integer right before the while condition.