Crash if delete addon after download

[FourGames]

Tested versions

Godot v4.4.beta2

System information

Godot v4.4.beta2 - Windows 11 (build 22631) - Multi-window, 3 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1070 (NVIDIA; 32.0.15.6614) - AMD Ryzen 5 3600 6-Core Processor (12 threads)

Issue description

Crash if delete addons after download, tested with multiple addons all the same.

Steps to reproduce

20250201-1449-23.1185138.mp4

Minimal reproduction project (MRP)

n/a

[Hilderin]

Pretty sure that's a side effect of #99844

When the addon is imported, the progress bar for the reimportation is inside the success dialog:

When the dialog is closed, the get_window of the progress dialog returns null propably because it was destroyed. That causes the get_last_exclusive_window to return null.

cc @KoBeWi

[KoBeWi]

#102237 will likely fix it.

[Maran23]

We should check if this is fixed by #102237, so we may close this ticket.

[Hilderin]

Tested with a build from master and I'm not able to reproduce the error.
I still the progress bar inside the confirmation popup but it does not crash anymore.