Snapshot: a turned single-view picture is stretched to the 16:9 cell #248

In /snapshot.jpg (debug page), the single view's camera is stretched to the 16:9 cell when its picture is not 16:9, for example a slot turned 90° (Turn, 2.17) whose picture is portrait. On the screen the picture is correct: fitted, with black bars.

Seen on Aceline-1 with a 2560×1920 H.265 stream turned 90° (1920×2560 on screen), with and without Mirror. The long-press screenshot is correct (1920×2560).

Cause: Snapshots.render() copies each live view with PixelCopy straight into its cell rectangle (Copy.start(view, rect.width(), rect.height()), then drawBitmap(frame, null, rect)), so a picture of another aspect ratio is scaled to the cell's 16:9.

Fix: for the single view, give the cell the picture's aspect ratio and copy into the largest rectangle of that ratio inside the cell, centred, with black around it, as the screen shows it.