Tabs: fixed ImGuiTabBarFlags_FittingPolicyScroll not triggering (regression in 3ef6c84). (#3421, #8800)

imgui_widgets.cpp

@@ -9689,7 +9689,8 @@ static void ImGui::TabBarLayout(ImGuiTabBar* tab_bar)
     // Horizontal scrolling buttons
     // Important: note that TabBarScrollButtons() will alter BarRect.Max.x.
     const bool can_scroll = (tab_bar->Flags & ImGuiTabBarFlags_FittingPolicyScroll) || (tab_bar->Flags & ImGuiTabBarFlags_FittingPolicyMixed);
-    tab_bar->ScrollButtonEnabled = ((width_all_tabs_after_min_width_shrink > tab_bar->BarRect.GetWidth() && tab_bar->Tabs.Size > 1) && !(tab_bar->Flags & ImGuiTabBarFlags_NoTabListScrollingButtons) && can_scroll);
+    const float width_all_tabs_to_use_for_scroll = (tab_bar->Flags & ImGuiTabBarFlags_FittingPolicyScroll) ? tab_bar->WidthAllTabs : width_all_tabs_after_min_width_shrink;
+    tab_bar->ScrollButtonEnabled = ((width_all_tabs_to_use_for_scroll > tab_bar->BarRect.GetWidth() && tab_bar->Tabs.Size > 1) && !(tab_bar->Flags & ImGuiTabBarFlags_NoTabListScrollingButtons) && can_scroll);
     if (tab_bar->ScrollButtonEnabled)
         if (ImGuiTabItem* scroll_and_select_tab = TabBarScrollingButtons(tab_bar))
         {