Fix handling of unicode filenames in usb_install_pc.py (#143)

tools/usb_install_pc.py

@@ -101,8 +101,9 @@ def send_nsp_list(nsp_dir, out_ep):
 
     # Add all files with the extension .nsp in the provided dir
     for nsp_path in [f for f in nsp_dir.iterdir() if f.is_file() and (f.suffix in EXTS)]:
-        nsp_path_list.append(nsp_path.__str__() + '\n')
-        nsp_path_list_len += len(nsp_path.__str__()) + 1
+        nsp_path = bytes(nsp_path.__str__(), 'utf8') + b'\n'
+        nsp_path_list.append(nsp_path)
+        nsp_path_list_len += len(nsp_path)
 
     print('Sending header...')