Automatically fallback to DIRECT when PAC unavailable

[SamuelePilleri]

When the configured PAC file is unavailable Windows automatically reverts to DIRECT connections, which is useful for example when connecting the work laptop to home Wi-Fi.
This commit mimics said behaviour.

[genotrance]

Thanks for the PR.

This change reverts to DIRECT if the PAC javascript parsing fails for some reason, but it could fail for other reasons. If PAC file doesn't exist or URL fails connect or load in pac.py (e.g. see #167), exception will be raised and not caught for first connection.

px/px/pac.py

Lines 40 to 53 in faaa57c

	def load_jsfile(self, jsfile):
	"Load specified JS file into this context"
	dprint("Loading PAC file: " + jsfile)
	with open(jsfile) as js:
	self.ctxt.eval(js.read())
	def load_url(self, jsurl):
	dprint("Loading PAC url: " + jsurl)
	c = Curl(jsurl)
	c.set_debug()
	c.buffer()
	c.set_follow()
	if c.perform():
	self.ctxt.eval(c.get_data())

wproxy.py code below does not handle failures for the first time and subsequent calls will have self.pac != None. This will be handled by your change but could be cleaner. Maybe not set self.pac if loading failed.

px/px/wproxy.py

Lines 247 to 256 in faaa57c

	if self.pac is None:
	# Load PAC file
	self.pac = Pac(debug_print = dprint)
	if self.servers[0].startswith("http"):
	self.pac.load_url(self.servers[0])
	else:
	self.pac.load_jsfile(self.servers[0])
	if self.pac is not None:
	return parse_proxy(self.pac.find_proxy_for_url(url, netloc[0])), netloc, path

Might be more cases but this is what stands out right now.