utils: raspberrypi: ctt: Fix NaNs in chromatic aberration tables NaNs can appear if no black dots can be found and analysed in a particular region of the calibration image. There needs to be at least one such dot in every 8x8 cell covering the image. This is now detected, and an error message issued. No CAC tables are generated, so CAC is disabled. Signed-off-by: David Plowman <[email protected]>