iOS Llama Demo App crashes if it doesn't like the PTE name

[swolchok]

🐛 Describe the bug

75f1eea added an exit(1) and an error message that only shows up on the console, which is not discoverable if you aren't actively debugging the app. Instead, we should show a clean error message that does not terminate the app.

Versions

main

cc @shoumikhin @cbilgin @larryliu0820 @mergennachin @cccclai @helunwencser @jackzhxng

[shoumikhin]

@jackzhxng can you ptal?