Serial mouse, microtouch, and modem: Add some more sanity checks.

src/device/mouse_microtouch_touchscreen.c

@@ -322,6 +322,8 @@ void
 mtouch_write_to_host(void *priv)
 {
     mouse_microtouch_t *dev = (mouse_microtouch_t *) priv;
+    if (dev->serial == NULL)
+        goto no_write_to_machine;
     if ((dev->serial->type >= SERIAL_16550) && dev->serial->fifo_enabled) {
         if (fifo_get_full(dev->serial->rcvr_fifo)) {
             goto no_write_to_machine;

src/device/mouse_serial.c

@@ -142,6 +142,7 @@ sermouse_transmit_byte(mouse_t *dev, int do_next)
     if (dev->buf_pos == 0)
         dev->acc_time = 0.0;
 
+    if (dev->serial)
         serial_write_fifo(dev->serial, dev->buf[dev->buf_pos]);
 
     if (do_next) {

src/network/net_modem.c

@@ -434,7 +434,7 @@ host_to_modem_cb(void *priv)
 {
     modem_t *modem = (modem_t *) priv;
 
-    if (modem->in_warmup)
+    if (modem->in_warmup || (modem->serial == NULL))
         goto no_write_to_machine;
 
     if ((modem->serial->type >= SERIAL_16550) && modem->serial->fifo_enabled) {
@@ -621,11 +621,13 @@ modem_enter_idle_state(modem_t *modem)
         }
     }
 
+    if (modem->serial != NULL) {
         serial_set_cts(modem->serial, 1);
         serial_set_dsr(modem->serial, 1);
         serial_set_dcd(modem->serial, (!modem->dcdmode ? 1 : 0));
         serial_set_ri(modem->serial, 0);
     }
+}
 
 void
 modem_enter_connected_state(modem_t *modem)
@@ -640,9 +642,12 @@ modem_enter_connected_state(modem_t *modem)
     plat_netsocket_close(modem->serversocket);
     modem->serversocket = -1;
     memset(&modem->telClient, 0, sizeof(modem->telClient));
+
+    if (modem->serial != NULL) {
         serial_set_dcd(modem->serial, 1);
         serial_set_ri(modem->serial, 0);
     }
+}
 
 void
 modem_reset(modem_t *modem)
@@ -1391,6 +1396,7 @@ modem_cmdpause_timer_callback(void *priv)
             } else {
                 modem->ringing = true;
                 modem_send_res(modem, ResRING);
+                if (modem->serial != NULL)
                     serial_set_ri(modem->serial, !serial_get_ri(modem->serial));
                 modem->ringtimer            = 3000;
                 modem->reg[MREG_RING_COUNT] = 0;
@@ -1405,6 +1411,7 @@ modem_cmdpause_timer_callback(void *priv)
                 return;
             }
             modem_send_res(modem, ResRING);
+            if (modem->serial != NULL)
                 serial_set_ri(modem->serial, !serial_get_ri(modem->serial));
 
             modem->ringtimer = 3000;