Fix: private league fetch failure crashes the trader. (TradeQuery.lua:157: table index is nil) (Cloudflare)

[apYdr6uxv]

Fixes #9176 .

Description of the problem being solved:

When retrieving leagues, if the private leagues fetch fails, it takes down the trader, even if the public leagues retrieve worked.
This fix proposes that it should instead continue , with just the public leagues it could retrieve.

Error:

In download callback: Classes/TradeQuery.lua:157: table index is nil
stack traceback:
	Classes/TradeQuery.lua:157: in function 'callback'
	Classes/TradeQuery.lua:85: in function 'callback'
	Launch.lua:319: in function <Launch.lua:318>
	[C]: in function 'PCall'
	Launch.lua:230: in function <Launch.lua:222>
v2.65.0 master
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Cause

The public leagues fetch is done using the API, and bypasses this issue entirely.
The private leagues fetch is done using HTTP callout (because there is no API for this), and runs into Cloudflare, if unlucky.

The private leagues fetch may hit Cloudflare challenge pages.
This is not an expected response, hence the crash. (The contents will be "Enable Javascript and cookies to continue")

This may not always happen, depending on how Cloudflare feels about you. (i.e. flaky repro)
Using a VPN might make it easier to reproduce.

The first sign of trouble is your trader window has no leagues populated.
The actual crash is produced on Get Currencies Conversion Rates or so.

Other changes

• flow changes: some guard against "missing leagues" state

Steps taken to verify a working solution:

• "works here"™
• ran docker tests

Link to a build that showcases this PR:

n/a

Before screenshot:

n/a

After screenshot:

n/a

[vaisest]

Superceded by #9812