Exit on imagemagick failure

gifcap.sh

@@ -73,6 +73,7 @@ if test -z "$output"; then
 	output="captioned-`basename "$input"`"
 fi
 
+
 if ! test -f "$input"; then
 	echo "$name: $input not found"
 	exit 1
@@ -88,7 +89,7 @@ convert \
 	-pointsize 55 -size "$captionWidth" -gravity Center \
 	caption:"$caption" \
 	-bordercolor white -border 20x20 \
-	"$captionTemp"
+	"$captionTemp" || exit 1
 
 echo "$name: compositing over $input..."
 # https://www.imagemagick.org/discourse-server/viewtopic.php?t=33797
@@ -97,7 +98,7 @@ convert \
 	-background white \( "$input" -coalesce \) \
 	-set page "%[fx:u.w]x%[fx:u.h+v.h]+%[fx:t?(u.w-v.w)/2:0]+%[fx:t?u.h:0]" -coalesce \
 	null: -insert 1 -layers composite -layers optimize \
-	"$output"
+	"$output" || exit 1
 
 rm "$captionTemp"
 echo "$name: done!"