Geocoding error handling

[sronveaux]

Here's some kind of follow-up to #343 where a flaky behaviour was observed during Geocoder unit tests.
Sometimes a strange error was thrown : TypeError: this.results.forEach is not a function

This happened from the query function inside the GeocoderController called from the Geocoder.vue component where the actual request was made like this:

try {
  const response = await json(ajax);
  return this.provider.handleResponse(response)
} catch (err) {
  return err
}

But with this code, if the underlying fetch was in error, the exception was caught then returned which made the Promise from the Geocoder component resolve instead of reject. So the error was considered as a result but was an Error instance instead of the expected Array of results...

This was simply corrected by removing the try - catch. If an error is thrown, it is practically caught inside the querySelections method of the Geocoder component as planned first.

The other unit tests for the geocoder have been slightly refactored to use a fake request instead of doing multiple API calls to Nominatim.
Some could argue that there is still a test making a real request and that this shouldn't be done inside unit tests but as this is the one which unveiled the bug corrected in #343 I thought making a real request was valuable in this case.

Please note that this final implementation is perhaps not the best one (onQueryError() does nothing except making a call to trace()) but the bug is corrected and the component should behave as it was designed at first...

[chrismayer]

Thanks for this @sronveaux. I just tested your change and this works quite well.