Mentions window: filter list when we part a chan

Should some other client part a chan, then we need to clean
up the list from the mentions window in case it's open in ours.

client/js/socket-events/part.js

@@ -12,10 +12,14 @@ socket.on("part", function (data) {
 
 	const channel = store.getters.findChannel(data.chan);
 
-	if (channel) {
-		channel.network.channels.splice(
-			channel.network.channels.findIndex((c) => c.id === data.chan),
-			1
-		);
+	if (!channel) {
+		return;
 	}
+
+	channel.network.channels.splice(
+		channel.network.channels.findIndex((c) => c.id === data.chan),
+		1
+	);
+
+	store.dispatch("partChannel", channel);
 });

client/js/store.js

@@ -130,6 +130,12 @@ const store = new Vuex.Store({
 			state.messageSearchResults = value;
 		},
 	},
+	actions: {
+		partChannel({commit, state}, netChan) {
+			const mentions = state.mentions.filter((msg) => !(msg.chanId === netChan.channel.id));
+			commit("mentions", mentions);
+		},
+	},
 	getters: {
 		findChannelOnCurrentNetwork: (state) => (name) => {
 			name = name.toLowerCase();