maintain previous behavior

selfdrive/car/car_helpers.py

@@ -67,19 +67,20 @@ def can_fingerprint(logcan: SimpleNamespace) -> tuple[str | None, dict[int, dict
           if can.src == b and can.address < 0x800 and can.address not in (0x7df, 0x7e0, 0x7e8):
             candidate_cars[b] = eliminate_incompatible_cars(can, candidate_cars[b])
 
-      # if we only have one car choice and the time since we got our first
-      # message has elapsed, exit
-      for b in candidate_cars:
-        if len(candidate_cars[b]) == 1 and frame > FRAME_FINGERPRINT:
-          # fingerprint done
-          car_fingerprint = candidate_cars[b][0]
-
-      # bail if no cars left or we've been waiting for more than 2s
-      failed = (all(len(cc) == 0 for cc in candidate_cars.values()) and frame > FRAME_FINGERPRINT) or frame > 200
-      succeeded = car_fingerprint is not None
-      done = failed or succeeded
-
-      frame += 1
+      if len(can_packet) > 0:
+        # if we only have one car choice and the time since we got our first
+        # message has elapsed, exit
+        for b in candidate_cars:
+          if len(candidate_cars[b]) == 1 and frame > FRAME_FINGERPRINT:
+            # fingerprint done
+            car_fingerprint = candidate_cars[b][0]
+
+        # bail if no cars left or we've been waiting for more than 2s
+        failed = (all(len(cc) == 0 for cc in candidate_cars.values()) and frame > FRAME_FINGERPRINT) or frame > 200
+        succeeded = car_fingerprint is not None
+        done = failed or succeeded
+
+        frame += 1
 
   return car_fingerprint, finger