CLI crashes when attaching to a non running iOS app

[DimitarTachev]

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 5.1.0
• Cross-platform modules: 5.1.0
• Android Runtime: 5.1.0
• iOS Runtime: 5.1.0

To Reproduce

1. Create a hello world js app.
2. tns debug ios
3. Close the app on the device/simulator.
4. Open the debug URL in order to start debugging.
5. The CLI will crash.

Expected behavior
The CLI should warn you that the app is not started without crashing.