Ignore all content until the first { character

[Robert-M-Muench]

Sometimes JSON files contain prolog content generated by external tools (even this is not standard) and on those files FX fails currently with an error.

It would be nice to just ignore everything until the first { is seen.

[antonmedv]

This is possible, but json file can start not only with a {, but also with [. And all of next files are json:

null

true

false

"str"

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