check for USB ready before reading usb_cdc instead of checking for serial connected

Author: Neradoc

shared-module/usb_cdc/Serial.c

@@ -19,7 +19,7 @@ size_t common_hal_usb_cdc_serial_read(usb_cdc_serial_obj_t *self, uint8_t *data,
     // Read up to len bytes immediately.
     // The number of bytes read will not be larger than what is already in the TinyUSB FIFO.
     uint32_t total_num_read = 0;
-    if (tud_cdc_n_connected(self->idx)) {
+    if (tud_ready()) {
         total_num_read = tud_cdc_n_read(self->idx, data, len);
     }
 
@@ -48,7 +48,7 @@ size_t common_hal_usb_cdc_serial_read(usb_cdc_serial_obj_t *self, uint8_t *data,
             data += num_read;
 
             // Try to read another batch of bytes.
-            if (tud_cdc_n_connected(self->idx)) {
+            if (tud_ready()) {
                 num_read = tud_cdc_n_read(self->idx, data, len);
             }
             total_num_read += num_read;