Update generate_notification_images.sh: minor formatting changes

scripts/generate_notification_images.sh

@@ -6,11 +6,11 @@
 # This is quick - on a Pi 4 it takes about one second per image.
 
 # Allow this script to be executed manually, which requires several variables to be set.
-[[ -z ${ALLSKY_HOME} ]] && export ALLSKY_HOME="$(realpath "$(dirname "${BASH_ARGV0}")/..")"
-ME="$(basename "${BASH_ARGV0}")"
+[[ -z ${ALLSKY_HOME} ]] && export ALLSKY_HOME="$( realpath "$( dirname "${BASH_ARGV0}" )/.." )"
+ME="$( basename "${BASH_ARGV0}" )"
 
-#shellcheck disable=SC2086 source-path=.
-source "${ALLSKY_HOME}/variables.sh"	|| exit ${ALLSKY_ERROR_STOP}
+#shellcheck source-path=.
+source "${ALLSKY_HOME}/variables.sh"	|| exit "${ALLSKY_ERROR_STOP}"
 
 readonly ALL_EXTS="jpg png"		# all the image filename extensions we support
 
@@ -35,8 +35,7 @@ function usage_and_exit()
 		echo "  '--size XxY' creates images that are X by Y pixels.  Default: ${DEFAULT_IMAGE_SIZE} pixels."
 		echo
 	) >&2
-	# shellcheck disable=SC2086
-	exit ${RET}
+	exit "${RET}"
 }
 
 # Check arguments
@@ -159,8 +158,7 @@ function make_image()
 	done
 }
 
-which mogrify > /dev/null
-if [[ $? -ne 0 ]]; then
+if ! which mogrify > /dev/null ; then
 	# Testing for mogrify which seems like a much more distinctive executable
 	# name than "convert". I assume that if "mogrify" is in the path, then
 	# ImageMagick is installed and "convert" will run ImageMagick and not some