Catch race condition when removing event handlers

aleksis/core/frontend/mixins/aleksis.js

@@ -22,15 +22,19 @@ const aleksisMixin = {
   beforeDestroy() {
     // Unregister all safely added event listeners as to not leak them
     for (let trackedEvent in this.$data.$_aleksis_safeTrackedEvents) {
-      console.debug(
-        "Removing handler for %s on %o",
-        trackedEvent.event,
-        trackedEvent.target
-      );
-      trackedEvent.target.removeEventListener(
-        trackedEvent.event,
-        trackedEvent.handler
-      );
+      if (trackedEvent.target) {
+        console.debug(
+          "Removing handler for %s on %o",
+          trackedEvent.event,
+          trackedEvent.target
+        );
+        trackedEvent.target.removeEventListener(
+          trackedEvent.event,
+          trackedEvent.handler
+        );
+      } else {
+        console.debug("Target already removed while removing event handler");
+      }
     }
   },
 };