tm: Fix invalid memory access on $T_id reads

Reported by Stepan Pologov.

Fixes #1326

(cherry picked from commit dbc1fed)

modules/tm/tm.c

@@ -2213,8 +2213,8 @@ static int pv_get_t_id(struct sip_msg *msg, pv_param_t *param,
 															pv_value_t *res)
 {
 #define INTasHEXA_SIZE (sizeof(int)*2)
+	static char buf[INTasHEXA_SIZE+1+INTasHEXA_SIZE];
 	struct cell *t;
-	char buf[INTasHEXA_SIZE+1+INTasHEXA_SIZE];
 	char *p;
 	int size;