Fix #5015: Cannot read property 'then' of null

extensions/typescript/src/features/bufferSyncSupport.ts

@@ -89,6 +89,9 @@ export default class BufferSyncSupport {
 		this.diagnosticDelayer = new Delayer<any>(100);
 
 		this.syncedBuffers = Object.create(null);
+	}
+
+	public listen(): void {
 		workspace.onDidOpenTextDocument(this.onDidAddDocument, this, this.disposables);
 		workspace.onDidCloseTextDocument(this.onDidRemoveDocument, this, this.disposables);
 		workspace.onDidChangeTextDocument(this.onDidChangeDocument, this, this.disposables);

extensions/typescript/src/typescriptMain.ts

@@ -107,6 +107,7 @@ class LanguageProvider {
 
 		client.onReady().then(() => {
 			this.registerProviders(client);
+			this.bufferSyncSupport.listen();
 		}, () => {
 			// Nothing to do here. The client did show a message;
 		});
@@ -241,7 +242,6 @@ class LanguageProvider {
 		this.syntaxDiagnostics = Object.create(null);
 		this.bufferSyncSupport.reOpenDocuments();
 		this.bufferSyncSupport.requestAllDiagnostics();
-
 	}
 
 	public triggerAllDiagnostics(): void {

extensions/typescript/src/typescriptServiceClient.ts

@@ -204,7 +204,6 @@ export default class TypeScriptServiceClient implements ITypescriptServiceClient
 				});
 			} catch (error) {
 				reject(error);
-				this._onReady.reject();
 			}
 		});
 		this.serviceStarted(resendModels);