Selection-based refactorings should not appear when there is no selection

## Steps to reproduce

In the following code, place the editor caret after 'false'.

```C#
using System;

class C
{
    void M()
    {
        Console.WriteLine(false);
    }
}
```

## Expected  behavior
No lightbulb should appear

## Actual behavior
A lightbulb appears with Extract Method, Introduce Local, etc.