[fix] get_bang_url: handle ambiguous !!bangs without error

[return42]

What does this PR do?

[fix] get_bang_url: handle ambiguous !!bangs without error

Why is this change important?

An ambiguous bang like !!d raises an exception in function get_bang_url(). A
bang is only unique when the bang_definition from get_bang_definition_and_ac() is
a string / for a ambiguous bang the returned bang_definition is a dictionary.

How to test this PR locally?

make run

Search for !!d foo

Related issues

Reported-by: user @prg318 at #searxng:matrix.org on 2022/01/11

[return42]

This PR need some more work, the initial issue is fixed but there is another issue:

Bangs with a * suffix, e.g. !!d*:

{
    "c":"Online Services",
    "d":"www.joindiaspora.com",
    "r":0,
    "s":"Diaspora*",
    "sc":"Social",
    "t":"d*",
    "u":"https://www.joindiaspora.com/people?utf8=\u2713&q={{{s}}}"
}

will overwrite bangs with the same prefix, e.g. !!d

{
    "c":"Research",
    "d":"www.thefreedictionary.com",
    "r":5478,"s":"The Free Dictionary",
    "sc":"Academic",
    "t":"d",
    "u":"http://www.thefreedictionary.com/{{{s}}}"
}

I assume it is caused by the * default:

searxng/searxng_extra/update/update_external_bangs.py

Line 141 in 977e9a4

t = t.setdefault('*', bang_def_output)

[return42]

@dalf are you active working on #740 (comment) .. if not, I can have a look.

[dalf]

@dalf are you active working on #740 (comment)

not right now

I can have a look.

👍

[return42]

@dalf I fixed issue of the optimized digital trie in 7cdd314 / if you have time for a review.

[dalf]

Good catch.
Thank you!