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/InputBox.cpp

@@ -127,7 +127,7 @@ void InputBox::on_done(ExecResult result)
 
 ErrorOr<void> InputBox::build()
 {
-    auto main_widget = TRY(set_main_widget<Widget>());
+    auto main_widget = set_main_widget<Widget>();
     main_widget->set_layout<VerticalBoxLayout>(6, 6);
     main_widget->set_fill_with_background_color(true);