remove after_utc parameter when no signals found (#481)

src/components/Contexts/CANSignalsContext.jsx

@@ -32,6 +32,7 @@ export const CANSignalProvider = ({ token, children }) => {
   const [vin, setVIN] = useState(null);
   const [signals, setSignals] = useState([]);
   const [utc, setUtc] = useState(undefined);
+  const [hasFoundSignalsBefore, setHasFoundSignalsBefore] = useState(false);
 
   useInterval(
     () => {
@@ -55,14 +56,15 @@ export const CANSignalProvider = ({ token, children }) => {
       if (mostRecentTimestamp) {
         setUtc(new Date(mostRecentTimestamp).getTime() - 50); // apply slight offset to ensure last CAN Signals sent before sleep are returned.
       } else {
-        setUtc(new Date().getTime());
+        setUtc(undefined);
       }
 
       const items = transformSignals(result.data);
 
       if (items.length > 0) {
         setSignals(items);
-      } else {
+        setHasFoundSignalsBefore(true)
+      } else if (!hasFoundSignalsBefore) {
         setSignals([BlankSignal("No signals")]);
       }
     } catch (e) {
@@ -73,7 +75,7 @@ export const CANSignalProvider = ({ token, children }) => {
   return (
     <CANSignalContext.Provider
       value={{
-        queryDate: new Date(utc).toLocaleTimeString(),
+        queryDate: utc && new Date(utc).toLocaleTimeString(),
         signals,
         setVIN,
         delays,