appimage-exec.sh parses its arguments with getopts, so we need to
delimit arguments intended for the wrapped executable with ‘--’, in
case some of them begin with ‘-’.
Without this fix, a wrapped application like Zulip Desktop can’t be
opened the normal way using the .desktop file, which includes
‘Exec=zulip --no-sandbox %U’ (as per the electron-builder default):
$ gtk-launch zulip.desktop
/usr/bin/appimage-exec.sh: illegal option -- -
Usage: appimage-run [appimage-run options] <AppImage> [AppImage options]
[…]
Signed-off-by: Anders Kaseorg <andersk@mit.edu>