Memleak in sds.c:40

There's a possible memleak and NULL ptr usage in sds.c:40 in `sdssplitargs`:

```c
vector = s_realloc(vector,((*argc)+1)*sizeof(char*));
vector[*argc] = current;
```

Realloc here might return NULL and thus NULLify `vector` while losing the reference to original object. I believe something like the following should be done:
```c
char** new_vector = s_realloc(vector,((*argc)+1)*sizeof(char*));
if (new_vector == NULL) goto err;
vector = new_vector;
vector[*argc] = current;
```