Ensure xterm exists before creating WindowsShellHelper

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

@@ -153,16 +153,16 @@ export class TerminalInstance implements ITerminalInstance {
 		this._initDimensions();
 		this._createProcess();
 
-		if (platform.isWindows) {
-			this._processReady.then(() => {
-				if (!this._isDisposed) {
-					this._windowsShellHelper = new WindowsShellHelper(this._processId, this, this._xterm);
-				}
-			});
-		}
-
 		this._xtermReadyPromise = this._createXterm();
 		this._xtermReadyPromise.then(() => {
+			if (platform.isWindows) {
+				this._processReady.then(() => {
+					if (!this._isDisposed) {
+						this._windowsShellHelper = new WindowsShellHelper(this._processId, this, this._xterm);
+					}
+				});
+			}
+
 			// Only attach xterm.js to the DOM if the terminal panel has been opened before.
 			if (_container) {
 				this.attachToElement(_container);