Handle signals not present in the __editor block in the json

[kreghek]

Describe the bug
For reasons described in #45 I added signals to a text node using text editor. But the dialogue editor starts to crush after it.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
Can you create signal's __editor information with defaults?

** Files**
Everything generated by LE Dialogue Editor (.cfg, .json etc.)

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Windows
• Version 4

Additional context
Add any other context about the problem here.