[dev-todo-mvvm-live-kotlin] App crashes when adding task with empty title or description

`saveTask()` function of `AddEditTaskViewModel.kt` is calling `Task(title.get(), description.get())` which causes crash when adding new task with title or description being empty.

Start by reading saveTask() in AddEditTaskViewModel.kt and reproduce adding a task with an empty title, an empty description, and both empty. Done means these cases no longer crash; the expected handling of the empty values is not specified in the issue.

Written by the indexing model from the issue text.