LibGUI: Fix Splitter sometimes not working after widgets were resized

We need to skip over widgets that are not visible as the layout does
not update their location. This fixes finding the correct widgets
surrounding the splitter.

Fixes #3491

Libraries/LibGUI/Splitter.cpp

@@ -86,23 +86,30 @@ void Splitter::leave_event(Core::Event&)
 bool Splitter::get_resize_candidates_at(const Gfx::IntPoint& position, Widget*& first, Widget*& second)
 {
     int x_or_y = position.primary_offset_for_orientation(m_orientation);
+    Widget* previous_widget = nullptr;
+    bool found_candidates = false;
+    for_each_child_widget([&](auto& child_widget) {
+        if (!child_widget.is_visible()) {
+            // We need to skip over widgets that are not visible as they
+            // are not necessarily in the correct location (anymore)
+            return IterationDecision::Continue;
+        }
+        if (!previous_widget) {
+            previous_widget = &child_widget;
+            return IterationDecision::Continue;
+        }
 
-    auto child_widgets = this->child_widgets();
-    if (child_widgets.size() < 2)
-        return false;
-
-    for (size_t i = 0; i < child_widgets.size() - 1; ++i) {
-        auto* first_candidate = child_widgets[i];
-        auto* second_candidate = child_widgets[i + 1];
-
-        if (x_or_y > first_candidate->content_rect().last_edge_for_orientation(m_orientation)
-            && x_or_y <= second_candidate->content_rect().first_edge_for_orientation(m_orientation)) {
-            first = first_candidate;
-            second = second_candidate;
-            return true;
+        if (x_or_y > previous_widget->content_rect().last_edge_for_orientation(m_orientation)
+            && x_or_y <= child_widget.content_rect().first_edge_for_orientation(m_orientation)) {
+            first = previous_widget;
+            second = &child_widget;
+            found_candidates = true;
+            return IterationDecision::Break;
         }
-    }
-    return false;
+
+        return IterationDecision::Continue;
+    });
+    return found_candidates;
 }
 
 void Splitter::mousedown_event(MouseEvent& event)