components/app: switch to server buffer on close only if active

If the buffer that's being closed is not the active one, there's no
point in switching the user away to another buffer.

components/app.js

@@ -1298,7 +1298,9 @@ export default class App extends Component {
 			}
 			// fallthrough
 		case BufferType.NICK:
-			this.switchBuffer({ name: SERVER_BUFFER });
+			if (this.state.activeBuffer === buf.id) {
+				this.switchBuffer({ name: SERVER_BUFFER });
+			}
 			this.setState((state) => {
 				let buffers = new Map(state.buffers);
 				buffers.delete(buf.id);