skip can_read logic if empty

src/main.c

@@ -118,6 +118,8 @@ void read_can(Tel *t, int soc) {
         struct can_frame frame;
         int nbytes = read(soc, &frame, sizeof(struct can_frame));
 
+        if (nbytes < 0) return; // -1 EAGAIN means empty
+
         if (nbytes > 0) {
 
                 switch (frame.can_id) {