Fix off-by-one error when truncating buffer

The __receive_buffer is always truncated by
[chars_processed_successfully + 1:].  When a partial socketcand frame is
received, chars_processed_successfully is 0, and this results in 1
character being discarded. This will be the '<' character, and thus when
the rest of the frame is received, it will be treated as a bad frame,
and discarded.

can/interfaces/socketcand/socketcand.py

@@ -191,9 +191,7 @@ def _recv_internal(self, timeout):
                     self.__message_buffer.append(parsed_can_message)
                 buffer_view = buffer_view[end + 1 :]
 
-            self.__receive_buffer = self.__receive_buffer[
-                chars_processed_successfully + 1 :
-            ]
+            self.__receive_buffer = self.__receive_buffer[chars_processed_successfully:]
             can_message = (
                 None
                 if len(self.__message_buffer) == 0