some norm and malloc protection

srcs/exec.c

@@ -0,0 +1,19 @@
+#include "philo.h"
+
+void	*philo_exec(void *arg)
+{
+	t_philo	*philo;
+	int		nbr;
+
+	philo = (t_philo*)arg;
+	nbr = philo->philo_nbr;
+
+	pthread_mutex_lock(&mutex);
+	write(1, "-", 1);
+	ft_putnbr_fd(nbr, 1);
+	write(1, "\n", 1);
+	pthread_mutex_unlock(&mutex);
+
+	return (NULL);
+}
+