Fix: Prevent race condition in toast (#3443)

src/mixins/socket.js

@@ -182,6 +182,7 @@ export default {
                 // Also toast
                 if (data.important) {
 
+                    if (this.monitorList[data.monitorID] !== undefined) {
                         if (data.status === 0) {
                             toast.error(`[${this.monitorList[data.monitorID].name}] [DOWN] ${data.msg}`, {
                                 timeout: false,
@@ -193,6 +194,7 @@ export default {
                         } else {
                             toast(`[${this.monitorList[data.monitorID].name}] ${data.msg}`);
                         }
+                    }
 
                     if (! (data.monitorID in this.importantHeartbeatList)) {
                         this.importantHeartbeatList[data.monitorID] = [];