[BUG] It's possible to add an empty action

[ptrckbp]

Describe the bug

You can click add action without anything

To Reproduce
Steps to reproduce the behavior:

1. Go to flow
2. Create a node
3. Click "+" sign then add action
4. See action created

Expected behavior
Form validation should catch this. The Add action button should be disabled unless there is something to add.

Environment (please complete the following information):

• OS: macOS
• Browser Chrome
• Browser Version Version 92.0.4515.131 (Official Build) (x86_64)
• Botpress Version 12.25.0
• NodeJS 12.13.0

Additional context
This will break the flow at the added location. Since it's an add function rather than an update function, I think in most cases people should notice it.