Check failure + crash caused by saving project while adding ACE's

Description

Construct 2 shows an error message and closes itself when adding new ACE's, at the exact moment while saving a project. This issue could be the leading cause of crashes related to auto-saving, since there is a chance of an auto-save occurring at one of those exact moments.

Below is a way to brute force this crash by manually saving using the KB shortcut.

Reproduction

1. Create new Construct 2 project
2. Save project to disk (capx or project folder doesn't matter)
3. Open event sheet and add dummy event to enable saving
4. Add an action by clicking "add action", while pressing CTRL+S at the same time (IMPORTANT: finish the process of adding an action!)
5. Notice error message followed by a crash or Construct 2 straight up closing itself

Error Message Screenshot (add action + save)

Version

Tested and could reproduce using Construct 2 r268 on Windows 7.

I can't follow this step:

> Add an action by clicking "add action", while pressing CTRL+S at the same time (IMPORTANT: finish the process of adding an action!)

How do you do these two things at the same time? Construct does not let you. When you click "add action" a modal dialog appears, which prevents saving. Once the modal dialog is closed, you can save again, and that seems to work correctly.

I tried to reproduce this in r272 but there is no error message. I will try to reproduce this again in the next beta cycle, since there have been a lot of updates.

The reproduction in general is very precise and you have to press CTRL+S just a few milliseconds before clicking "add action". Again, I'll try to reproduce this and upload a video of it happening in the next beta cycle.