[json] wait for onReady before using client

extensions/json/client/src/jsonMain.ts

@@ -68,6 +68,8 @@ export function activate(context: ExtensionContext) {
 
 		// Create the language client and start the client.
 		let client = new LanguageClient('json', localize('jsonserver.name', 'JSON Language Server'), serverOptions, clientOptions);
+		let disposable = client.start();
+		client.onReady().then(() => {
 			client.onTelemetry(e => {
 				if (telemetryReporter) {
 					telemetryReporter.sendTelemetryEvent(e.key, e.data);
@@ -84,9 +86,8 @@ export function activate(context: ExtensionContext) {
 				});
 			});
 
-		let disposable = client.start();
-
 			client.sendNotification(SchemaAssociationNotification.type, getSchemaAssociation(context));
+		});
 
 		// Push the disposable to the context's subscriptions so that the
 		// client can be deactivated on extension deactivation