Log file

Enable view log file only if a log file id is returned.

Test 1
 * Import a faulty image e.g. squig/data_repo/test_images_bad/multi-image-pixels.ome.tif 
 * check that the View log file button is active

Test 2
 *  import squig/data_repo/test_images_broken/broken_images_scenario/fails_at_processing/wrong-light-source-mk3.ome
* check that the View log file button is  not active
 
it cannot be null, it will -1 if not set.