Show Map in dataflash log viewer doesn't allow zooming to the same level as the main map

I sometimes find that the map in the Dataflash log viewer cannot zoom in far enough. Sometimes with small missions like those on a rover I would like to zoom in more. I think the map on the Data screen can zoom in much more.

Start by reproducing the zoom limit in the Dataflash log viewer and compare it with the map on the Data screen. Trace where each view sets its maximum zoom level; done means small rover missions can zoom the log-viewer map to the same level as the main map.

Written by the indexing model from the issue text.