Userland: Make Window::set_main_widget() non-fallible

Author: https://github.com/tcl3
Commit: 3aa49f268c
Pull-request: https://github.com/SerenityOS/serenity/pull/21152
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Applications/PixelPaint/LevelsDialog.cpp

@@ -18,7 +18,7 @@ LevelsDialog::LevelsDialog(GUI::Window* parent_window, ImageEditor* editor)
     set_title("Levels");
     set_icon(parent_window->icon());
 
-    auto main_widget = set_main_widget<GUI::Widget>().release_value_but_fixme_should_propagate_errors();
+    auto main_widget = set_main_widget<GUI::Widget>();
     main_widget->load_from_gml(levels_dialog_gml).release_value_but_fixme_should_propagate_errors();
 
     resize(305, 202);