[NeedNewTest] 42filechecker doesn't check memory allocation on strjoin 

```
#include "libft.h"

char	*ft_strjoin(char const *s1, char const *s2)
{
	char	*res;

	if (s1 == NULL || s2 == NULL)
		return (NULL);
	if (!(res = ft_strnew(ft_strlen((char *)s1 + ft_strlen((char *)s2 + 1))))) // +1 is very bad but 42fc don' t check it!
		return (NULL);
	res = ft_strcpy(res, s1);
	res = ft_strcat(res, s2);
	return (res);
}
```

Thx