zoom changed when converting a layer

[richlv]

this is a regression between 7777 and 7906.

previously, if a gpx layer was converted to data layer or data layer was converted to gpx, zoom was not changed. now, it zooms to the whole layer.

quite often i use conversion to remove a stray gps point. in that case i zoom in on that position and convert. now i have to find the location again, as i zooms to the whole layer.

additionally, if some layer like imagery is open, it starts to downloads lots of extra data, which is a bit of an extra concern on slow/metered connections :)

zooming to a layer, if desired is easy - one can just hit '2', thus this automatic zoom change seems to be more harmful than not.

the only revision that seems suspect is this :
@7817

fixed #10861 - Zoom to layer when opening new file (see #10860)

although i haven't tested it and it could be something else :)