tools/toolbox: Consistently handle option parsing failures

`getopt` already prints a message on parse errors, but it still
seems like good style to point to --help as we do elsewhere.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3113>

tools/toolbox/create-toolbox.sh

@@ -96,7 +96,7 @@ TEMP=$(getopt \
   --longoptions 'skip-mutter' \
   --longoptions 'set-default' \
   --longoptions 'help' \
-  -- "$@")
+  -- "$@") || die "Run $(basename $0) --help to see available options"
 
 eval set -- "$TEMP"
 unset TEMP

tools/toolbox/meson-build.sh

@@ -50,7 +50,7 @@ TEMP=$(getopt \
   --longoptions 'toolbox:' \
   --longoptions 'dist' \
   --longoptions 'help' \
-  -- "$@")
+  -- "$@") || die "Run $(basename $0) --help to see available options"
 
 eval set -- "$TEMP"
 unset TEMP