SeeedBus: Crash occsionally.

### Describe the bug
python-can crashes rarely with the error:
```
msg = self.bus.recv(0.0)
File "/nix/store/0amvifzhc5sv3p1b29dzwxd53njs74z3-python3.13-python-can-4.6.1/lib/python3.13/site-packages/can/bus.py", line 121, in recv
msg, already_filtered = self._recv_internal(timeout=time_left)
~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
File "/nix/store/0amvifzhc5sv3p1b29dzwxd53njs74z3-python3.13-python-can-4.6.1/lib/python3.13/site-packages/can/interfaces/seeedstudio/seeedstudio.py", line 279, in _recv_internal
end_packet = ord(self.ser.read())
TypeError: ord() expected a character, but string of length 0 found
```

### To Reproduce
Use a while true loop to open the device quickly.
For my use-case, I needed to implement a flush_rx_buffer() function on user-level:
Please ignore my comments in the code, they may be outdated.
```
def flush_rx_buffer(self):
"""Discarding the received buffer."""
# As python-can does not implement any discarding of old messages, see:
# https://github.com/hardbyte/python-can/issues/1721
# The recv(0.0) is probably a non-blocking function, see:
# https://python-can.readthedocs.io/en/3.3.2/interfaces/socketcan.html
# That non-blocking function should return immediately.
while True:
msg = self.bus.recv(0.0)
if msg is None:
return

````

### Expected behavior
Instead of a TypeError I expected to receive a None.

### Additional context

OS and version: NixOS
Python version: 3.13
python-can version: 4.6.1
python-can interface/s (if applicable): seeedstudio

I'm using an asus nuc 15, so quite a fast CPU. I don't remember this error to appear on the slow raspberry pi pico.

Traceback and logs

```python
def func():
return "hello, world!"
```