Fix NPE in Chrome Device (#42813)

packages/flutter_tools/lib/src/web/web_device.dart

@@ -61,7 +61,7 @@ class ChromeDevice extends Device {
 
   @override
   DeviceLogReader getLogReader({ApplicationPackage app}) {
-    return NoOpDeviceLogReader(app.name);
+    return NoOpDeviceLogReader(app?.name);
   }
 
   @override

packages/flutter_tools/test/general.shard/web/devices_test.dart

@@ -42,6 +42,7 @@ void main() {
     expect(chromeDevice.supportsScreenshot, false);
     expect(await chromeDevice.isLocalEmulator, false);
     expect(chromeDevice.getLogReader(app: mockWebApplicationPackage), isInstanceOf<NoOpDeviceLogReader>());
+    expect(chromeDevice.getLogReader(), isInstanceOf<NoOpDeviceLogReader>());
     expect(await chromeDevice.portForwarder.forward(1), 1);
   });