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/Libraries/LibGUI/MessageBox.cpp

@@ -150,7 +150,7 @@ bool MessageBox::should_include_no_button() const
 
 ErrorOr<void> MessageBox::build()
 {
-    auto main_widget = TRY(set_main_widget<Widget>());
+    auto main_widget = set_main_widget<Widget>();
     main_widget->set_fill_with_background_color(true);
     main_widget->set_layout<VerticalBoxLayout>(8, 6);