invalid path in OCIO env var causes UI to break

[edi-spaghetti]

While testing some setup I put the wrong path into my OCIO environment variables, and on launching xstudio got these errors:

[2023-03-01 17:31:59.825] [xstudio] [warning] virtual void xstudio::ui::qml::ModuleAttrsToQMLShim::init(caf::actor_system&) caf::sec::invalid_argument
[2023-03-01 17:31:59.855] [xstudio] [warning] virtual void xstudio::ui::qml::ModuleAttrsToQMLShim::init(caf::actor_system&) caf::sec::invalid_argument
[2023-03-01 17:31:59.856] [xstudio] [warning] virtual void xstudio::ui::qml::ModuleAttrsToQMLShim::init(caf::actor_system&) caf::sec::invalid_argument
[2023-03-01 17:31:59.859] [xstudio] [warning] virtual void xstudio::ui::qml::ModuleAttrsToQMLShim::init(caf::actor_system&) caf::sec::invalid_argument
*** unexpected message [id: 533, name: user.scheduled-actor]: message(xstudio::broadcast::broadcast_down_atom(), 191@EA6CE6C334CF53DE51E455BBB0EBCFE5B5D3897D#30902)
[2023-03-01 17:31:59.971] [xstudio] [warning] virtual void xstudio::ui::qml::ModuleAttrsToQMLShim::init(caf::actor_system&) caf::sec::invalid_argument
*** unhandled exception: [id: 255, name: PlayheadActor, exception typeid: std.runtime_error]: GlobalStore is not registered
*** unhandled exception: [id: 430, name: user.scheduled-actor, exception typeid: std.runtime_error]: GlobalStore is not registered
[2023-03-01 17:32:07.615] [xstudio] [warning] caf::mixin::actor_object<Base, EventId>::init(caf::actor_system&) [with Base = QObject; int EventId = 32337]::<lambda()>
*** unhandled exception: [id: 440, name: user.scheduled-actor, exception typeid: std.runtime_error]: GlobalStore is not registered
*** unhandled exception: [id: 447, name: user.scheduled-actor, exception typeid: std.runtime_error]: GlobalStore is not registered
*** unhandled exception: [id: 461, name: user.scheduled-actor, exception typeid: std.runtime_error]: GlobalStore is not registered
[2023-03-01 17:32:08.479] [xstudio] [warning] caf::mixin::actor_object<Base, EventId>::init(caf::actor_system&) [with Base = QObject; int EventId = 32337]::<lambda()>
*** unhandled exception: [id: 472, name: user.scheduled-actor, exception typeid: std.runtime_error]: GlobalStore is not registered
*** unhandled exception: [id: 478, name: user.scheduled-actor, exception typeid: std.runtime_error]: GlobalStore is not registered
[2023-03-01 17:32:34.075] [xstudio] [warning] Failed to save prefs caf::sec::invalid_argument
[2023-03-01 17:32:34.075] [xstudio] [warning] Failed to save prefs caf::sec::invalid_argument
[2023-03-01 17:32:34.075] [xstudio] [warning] Failed to save prefs caf::sec::invalid_argument

The UI then failed to load any of the dropdown menus.

This is fixed by having a valid ocio config in the OCIO variable, but it would be a much better user experience if it simply warned 'the OCIO variable is invalid' rather than breaking the entire application.