Fix memory leaks on failure

[MaxXor]

• in userland/client/listener.c is a memory leak in shell(int sock, char **args) when a large amount of arguments is submitted, it is fixed in a similar way like this: https://github.com/f0rb1dd3n/Reptile/blob/6bd476e38ebc15a5bd08a3457f14cf329978cad6/userland/client/client.c#L522-L528
• in userland/client/client.c and userland/client/listener.c is also a realloc memory leak in readline(void)
• in userland/shell.c is a memory leak in runshell(int client) when fork() failed

[f0rb1dd3n]

Thank you for reporting that!