zoom changed when converting a layer

[richlv]

this is a regression between r7777 and r7906.

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 :
r7817

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

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

[richlv]

another problem - download data + gpx (where there's lots of traces). for gpx, choose background option. do some other things... when gpx download finishes, zoom jumps to the gpx layer. should not :)

[richlv]

another problem : with mapillary plugin, when one downloads data layer, mapillary information is downloaded in the background. this can take a while, and if one zoom and pans around, once mapillary data is downloaded, it zooms to the new mapillary data.

all of thee together are fairly noticeable :)