Make sure the received DTMF duration is initialsed at the beginning, and if the…

Make sure the received DTMF duration is initialsed at the beginning, and if the realtime calllback is set or altered during operation of the detector.

libs/spandsp/src/dtmf.c

@@ -346,6 +346,7 @@ SPAN_DECLARE(void) dtmf_rx_set_realtime_callback(dtmf_rx_state_t *s,
 {
     s->realtime_callback = callback;
     s->realtime_callback_data = user_data;
+    s->duration = 0;
 }
 /*- End of function --------------------------------------------------------*/
 
@@ -395,6 +396,7 @@ SPAN_DECLARE(dtmf_rx_state_t *) dtmf_rx_init(dtmf_rx_state_t *s,
         if ((s = (dtmf_rx_state_t *) malloc(sizeof (*s))) == NULL)
             return  NULL;
     }
+    memset(s, 0, sizeof(*s));
     span_log_init(&s->logging, SPAN_LOG_NONE, NULL);
     span_log_set_protocol(&s->logging, "DTMF");
     s->digits_callback = callback;
@@ -547,6 +549,7 @@ SPAN_DECLARE(dtmf_tx_state_t *) dtmf_tx_init(dtmf_tx_state_t *s)
         if ((s = (dtmf_tx_state_t *) malloc(sizeof (*s))) == NULL)
             return  NULL;
     }
+    memset(s, 0, sizeof(*s));
     if (!dtmf_tx_inited)
         dtmf_tx_initialise();
     tone_gen_init(&(s->tones), &dtmf_digit_tones[0]);