UI fails to show any information on 502

[GregOriol]

The AJAX request to the test api returned an HTTP 502 for my failed test (valid hostname but port closed on ipv6/open on ipv4) and the UI failed to show any information, the loader was going indefinitely, nothing happening. At least some error message should be shown when there is an error during the test.

[turt2live]

ftr there is a console error, but that seems to be not enough for the UI to show something other than an infinite loading screen:

/federationtester/api/report?server_name=hispagatos.org:1 Failed to load resource: the server responded with a status of 524 ()
23:56:42.137 matrix.org/:1 Uncaught (in promise) SyntaxError: Unexpected token < in JSON at position 0