fix skipFirstRun at useCustomEvent in strict mode (#55)

Co-authored-by: Sándor Szilágyi <[email protected]>

applicationinsights-react-js/src/useTrackEvent.ts

@@ -1,7 +1,7 @@
 /**
-* ReactPlugin.ts
-* @copyright Microsoft 2019
-*/
+ * ReactPlugin.ts
+ * @copyright Microsoft 2019
+ */
 import ReactPlugin from "./ReactPlugin";
 import { Dispatch, SetStateAction, useEffect, useRef, useState } from "react";
 
@@ -15,6 +15,7 @@ export default function useCustomEvent<T>(
 ): AIReactCustomEvent<T> {
   const [data, setData] = useState(eventData);
   const firstRun = useRef(skipFirstRun);
+  const savedSkipFirstRun = useRef(skipFirstRun);
 
   useEffect(() => {
     if (firstRun.current) {
@@ -24,5 +25,11 @@ export default function useCustomEvent<T>(
     reactPlugin.trackEvent({ name: eventName }, data);
   }, [reactPlugin, data, eventName]);
 
+  useEffect(() => {
+    return () => {
+      firstRun.current = savedSkipFirstRun.current;
+    };
+  }, []);
+
   return setData as AIReactCustomEvent<T>;
 }