Blender import support is not properly validated before re-importing .blend file

[akien-mga]

Tested versions

• Reproducible in 4.3.rc1
• Not reproducible in 4.2.2.stable Also reproducible in 4.2.2.stable

System information

Fedora Linux 40 (KDE Plasma) - Wayland - Vulkan (Forward+) - dedicated AMD Radeon RX 7600M XT (RADV NAVI33) - AMD Ryzen 7 7840HS w/ Radeon 780M Graphics (16 Threads)

Issue description

There seems to be a regression in 4.3 with the validation of Blender file import support.
It's probably not too critical as it's a bit of an edge case, but it's a soft lock so still bad if users run into it.

If the Blender path is not configured, the dialog is shown when a new .blend file without .import file is encountered.
However, if a .blend file has already been imported in .godot and has an .import file, it won't trigger that logic, and the dialog won't be shown.

The editor at this point believes that it can open this file in the advanced importer, even though it doesn't know where to find Blender.

Double-clicking the file leads to:

ERROR: Could not create child process: 
   at: create_process (./drivers/unix/os_unix.cpp:704)

And an editor soft lock.

Steps to reproduce

• In a 4.3 project, configure the Blender executable path properly
• Add a .blend file and import it
• Remove the Blender executable path from the editor settings and reopen the project
• Double click the .blend file -> freeze

Minimal reproduction project (MRP)

testreimportbug.zip