Properly dispose of WindowsShellHelper

Fixes #33536

src/vs/workbench/parts/terminal/electron-browser/windowsShellHelper.ts

@@ -3,7 +3,6 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import * as cp from 'child_process';
 import * as platform from 'vs/base/common/platform';
 import { TPromise } from 'vs/base/common/winjs.base';
 import { Emitter, debounceEvent } from 'vs/base/common/event';
@@ -17,7 +16,6 @@ let windowsProcessTree;
 export class WindowsShellHelper {
 	private _childProcessIdStack: number[];
 	private _onCheckShell: Emitter<TPromise<string>>;
-	private _wmicProcess: cp.ChildProcess;
 	private _isDisposed: boolean;
 
 	public constructor(
@@ -60,6 +58,9 @@ export class WindowsShellHelper {
 	}
 
 	private traverseTree(tree: any): string {
+		if (!tree) {
+			return '';
+		}
 		if (SHELL_EXECUTABLES.indexOf(tree.name) === -1) {
 			return tree.name;
 		}
@@ -84,15 +85,15 @@ export class WindowsShellHelper {
 
 	public dispose(): void {
 		this._isDisposed = true;
-		if (this._wmicProcess) {
-			this._wmicProcess.kill();
-		}
 	}
 
 	/**
 	 * Returns the innermost shell executable running in the terminal
 	 */
 	public getShellName(): TPromise<string> {
+		if (this._isDisposed) {
+			return TPromise.as('');
+		}
 		return new TPromise<string>(resolve => {
 			windowsProcessTree(this._rootProcessId, (tree) => {
 				resolve(this.traverseTree(tree));