fix(esp_driver_usb_serial_jtag): check USJ accessibility before read/write

Add connection checks to usb_serial_jtag_write and usb_serial_jtag_read
functions to return -EIO error code when the USB Serial JTAG is not
connected.

components/esp_driver_usb_serial_jtag/src/usb_serial_jtag_vfs.c

@@ -182,6 +182,10 @@ static int usb_serial_jtag_rx_char_no_driver(int fd)
 
 static ssize_t usb_serial_jtag_write(int fd, const void * data, size_t size)
 {
+    if (!usb_serial_jtag_is_connected()) {
+        // TODO: IDF-14303
+        return -1;
+    }
     const char *data_c = (const char *)data;
     /*  Even though newlib does stream locking on each individual stream, we need
      *  a dedicated lock if two streams (stdout and stderr) point to the
@@ -226,6 +230,10 @@ static void usb_serial_jtag_return_char(int fd, int c)
 
 static ssize_t usb_serial_jtag_read(int fd, void* data, size_t size)
 {
+    if (!usb_serial_jtag_is_connected()) {
+        // TODO: IDF-14303
+        return -1;
+    }
     assert(fd == USJ_LOCAL_FD);
     char *data_c = (char *) data;
     size_t received = 0;
@@ -349,6 +357,10 @@ static int usb_serial_jtag_wait_tx_done_no_driver(int fd)
 
 static int usb_serial_jtag_fsync(int fd)
 {
+    if (!usb_serial_jtag_is_connected()) {
+        // TODO: IDF-14303
+        return -1;
+    }
     _lock_acquire_recursive(&s_ctx.write_lock);
     int r = s_ctx.fsync_func(fd);
     _lock_release_recursive(&s_ctx.write_lock);