Fix Ferrum::Network::Response#loaded? for redirect response

[francisbeaudoin]

Issue

Fixes #321

Context

Redirect Ferrum::Network::Response are created within the Network.requestWillBeSent event:

ferrum/lib/ferrum/network.rb

Lines 358 to 366 in e2340b3

	# On redirects Chrome doesn't change `requestId` and there's no
	# `Network.responseReceived` event for such request. If there's already
	# exchange object with this id then we got redirected and params has
	# `redirectResponse` key which contains the response.
	if params["redirectResponse"]
	previous_exchange = select(request.id)[-2]
	response = Network::Response.new(@page, params)
	previous_exchange.response = response
	end

Additionally, the Network.loadingFinished event is where responses are marked as loaded = true:

ferrum/lib/ferrum/network.rb

Lines 386 to 392 in e2340b3

	@page.on("Network.loadingFinished") do |params|
	response = select(params["requestId"]).last&.response
	if response
	response.loaded = true
	response.body_size = params["encodedDataLength"]
	end

As redirect responses are sharing the same requestId and as that code is only selecting the last exchange response e.g. the final response, only that exchange response is marked as loaded?.

Proposed fix

Assigning loaded = true at the time that redirect response object is created.

Note: Unfortunately I'm running into issues executing tests locally so I didn't add any. Per my quick testing, it looks to be solving the aforementioned issue.