GeocodeProvider: Return more useful error msg when it's disabled

[luk1337]

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[Fs00]

Thanks for this, I remember being puzzled by that "disabled" message the first time I saw it.

@mar-v-in I've always wondered: why is the geocoding API disabled by default? It isn't necessarily called with the user location, and even in that case I think that OSM can be considered a trusted provider.
When disabled, apps that rely on it are likely to crash. One notable example where this happens is a popular payments app in Italy, which uses the reverse geocoder to let the user search for a real world location to then list merchants in its proximity.