Minor fixes regarding websockets

.gitignore

@@ -2,3 +2,4 @@
 node_modules
 package-lock.json
 sessions.json
+client_sessions.json

main.js

@@ -1024,6 +1024,9 @@ class WSServer {
 				delete this.clients[sessionId][index];
 			}
 			this.clients[sessionId] = this.clients[sessionId].filter(Boolean);
+			if (this.clients[sessionId].length === 0) {
+				delete this.clients[sessionId];
+			}
 		}
 	}
 
@@ -1044,14 +1047,14 @@ class WSServer {
 	}
 
 	pduEvent(sessionId, pdu) {
+		let clients = this.clients[sessionId];
+		if (!!clients) {
 			this.logger.log2(`Session with ID ${sessionId} fired PDU`);
 			let payload = {
 				type: 'pdu',
 				sessionId: sessionId,
 				value: pdu
 			}
-		let clients = this.clients[sessionId];
-		if (!!clients) {
 			this.logger.log2(`Broadcasting session with ID ${sessionId} to ${clients.length} clients`);
 			clients.forEach(client => {
 				client.send(JSON.stringify(payload));