debug: null guard if the server crashes before the initialize response.

fixes #1156

src/vs/workbench/parts/debug/electron-browser/debugService.ts

@@ -500,6 +500,10 @@ export class DebugService extends ee.EventEmitter implements debug.IDebugService
 			linesStartAt1: true,
 			pathFormat: 'path'
 		}).then((result: DebugProtocol.InitializeResponse) => {
+			if (!this.session) {
+				return Promise.wrapError(new Error(nls.localize('debugAdapterCrash', "Debug adapter process has terminated unexpectedly")));
+			}
+
 			this.setStateAndEmit(debug.State.Initializing);
 			return configuration.request === 'attach' ? this.session.attach(configuration) : this.session.launch(configuration);
 		}).then((result: DebugProtocol.Response) => {

src/vs/workbench/parts/debug/node/rawDebugSession.ts

@@ -3,6 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
+import nls = require('vs/nls');
 import cp = require('child_process');
 import fs = require('fs');
 import net = require('net');
@@ -290,7 +291,7 @@ export class RawDebugSession extends v8.V8Protocol implements debug.IRawDebugSes
 		this.serverProcess = null;
 		this.cachedInitServer = null;
 		if (!this.stopServerPending) {
-			this.messageService.show(severity.Error, 'Debug adapter process has terminated unexpectedly');
+			this.messageService.show(severity.Error, nls.localize('debugAdapterCrash', "Debug adapter process has terminated unexpectedly"));
 		}
 		this.emit(debug.SessionEvents.SERVER_EXIT);
 	}