Since execl() is a variadic function, it requries a NULL-terminal to
indicate the end of its argument list, c.f. exec(3)
> The first argument, by convention, should point to the filename
> associated with the file being executed. The list of arguments *must*
> be terminated by a null pointer
This fixes the failure seen on aarch64 and i386, due to garbage data
being considered part of the variadic arguments.