Blender import: Correct exit code on Python exception

[kroketio]

When running Blender direct import, it executes some Python but does not check if it succeeded.

godot/modules/gltf/editor/editor_import_blend_runner.cpp

Lines 84 to 93 in 607b230

	static constexpr char PYTHON_SCRIPT_DIRECT[] = R"(
	import bpy, sys
	opts = %s
	if bpy.app.version < (3, 0, 0):
	print('Blender 3.0 or higher is required.', file=sys.stderr)
	bpy.ops.wm.open_mainfile(filepath=opts['path'])
	if opts['unpack_all']:
	bpy.ops.file.unpack_all(method='USE_LOCAL')
	bpy.ops.export_scene.gltf(**opts['gltf_options'])
	)";

Which goes to start_blender(...) and exitcode is checked to determine failure.

godot/modules/gltf/editor/editor_import_blend_runner.cpp

Lines 161 to 175 in 607b230

	Error EditorImportBlendRunner::start_blender(const String &p_python_script, bool p_blocking) {
	String blender_path = EDITOR_GET("filesystem/import/blender/blender_path");
	List<String> args;
	args.push_back("--background");
	args.push_back("--python-expr");
	args.push_back(p_python_script);
	Error err;
	if (p_blocking) {
	int exitcode = 0;
	err = OS::get_singleton()->execute(blender_path, args, nullptr, &exitcode);
	if (exitcode != 0) {
	return FAILED;
	}

However, Blender does not return exitcode 1 when the Python script fails: blender/issues/82494

There is --python-exit-code which returns the exitcode in the given value whenever the script fails:

$ blender --help
--python-exit-code <code>
        Set the exit-code in [0..255] to exit if a Python exception is raised
        (only for scripts executed from the command line), zero disables.

This PR adds the flag, as well as print the stderr of the Blender process for more clarity.

[fire]

looks ok.

[aaronfranke]

Makes sense to me. I did not test it.

[kroketio]

I did test it, should work for both Blender 3 and 4 major releases.

[Repiteo]

Thanks!