Godot: [Regression] GUT test window crash on running tests

[Xrayez]

Godot version:
Godot 3.1 alpha custom build 3a312db

OS/device including version:
Windows 10

Issue description:
I'm using GUT addon for unit testing. After compiling 3a312db the scene crashes when I try to run tests with this error:

ERROR: _get_socket_error: Socket error: 10054
At: drivers/unix/net_socket_posix.cpp:195

The crash might be difficult to reproduce. Turning on some exported scene options like should_maximize or should_print_to_console might increase the chance of the crash. In my other main game project the crash is consistent, but I fail to isolate the cause.

20725 introduced the regression.

@Calinou, what do you think might cause this? The gut test window uses TextEdit for printing testing info, this might trigger something bad. Maybe it's due to some uninitialized editor settings related to text edit?

Should be fixed with https://github.com/godotengine/godot/issues/24283#issuecomment-446597744

Steps to reproduce:

1. Download minimal project (fetched from https://github.com/bitwes/Gut/tree/godot_3_1)
2. Open the project, proceed to scenes/main.tscn and run this scene.
3. In the test window that appeared, press run button.
4. Depending on magical conditions, this should crash. If not, try restarting the editor.

Minimal reproduction project:
Gut.3.1.compatible.zip

[Xrayez]

I found the culprit! draw_indent_guides is uninitialized, that explains why the bug can't seem to be reproducible consistently. Simply init it in the TextEdit constructor. Not sure what would be the default value so waiting for @Calinou to fix it.

https://github.com/godotengine/godot/blob/4cb6b80090d60b11522e3af5e3732ab0b1336d72/scene/gui/text_edit.cpp#L6267-L6273