Fix retrieval of remote source logos in GeoNetwork harvesters.

[josegar74]

Logo retrieval was assuming that the logos extension was gif only, which is not the case, png and jpg formats are allowed also.

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[fxprunayre]

Looks fine. Can be tested with https://sextant.ifremer.fr/geonetwork/images/logos/b08fe709-1ced-4a07-8edf-06aa6ccdf2e3.gif vs https://sextant.ifremer.fr/geonetwork/images/logos/b08fe709-1ced-4a07-8edf-06aa6ccdf2e3.png

At some point, maybe we should consider adding a dedicated endpoint for source logo retrieval without relying on image extension.

[juanluisrp]

There ia a security issue in this code.

[josegar74]

@juanluisrp I have added in the harvester code to check that the logo doesn't contain bad path characters. See 4a6ef4b

I haven't update XmlRequest. For that we can do another pull request, probably sending also a base path so the code checks that the file path is inside the base path.

[josegar74]

@juanluisrp please check the latest commit: 8e53529