RangeSelect/MultiSelect: Added IMGUI_HAS_MULTI_SELECT define. Fixed right-click toggling selection without clearing active id, could lead to MarkItemEdited() asserting. Fixed demo.

imgui.h

@@ -2368,6 +2368,7 @@ struct ImGuiListClipper
 //   5) Call EndMultiSelect(). Save the value of ->RangeSrc for the next frame (you may convert the value in a format that is safe for persistance)
 //   6) Honor Clear/SelectAll/SetRange requests by updating your selection data. Always process them in this order (as you will receive Clear+SetRange request simultaneously)
 // If you submit all items (no clipper), Step 2 and 3 and will be handled by Selectable() on a per-item basis.
+#define IMGUI_HAS_MULTI_SELECT      // Multi-Select/Range-Select WIP branch // <-- This is currently _not_ in the top of imgui.h to prevent merge conflicts.
 struct ImGuiMultiSelectData
 {
     bool    RequestClear;           // Begin, End   // Request user to clear selection

imgui_widgets.cpp

@@ -6504,7 +6504,9 @@ void ImGui::MultiSelectItemFooter(ImGuiID id, bool* p_selected, bool* p_pressed)
     bool hovered = IsItemHovered(ImGuiHoveredFlags_AllowWhenBlockedByPopup);
     if (hovered && IsMouseClicked(1))
     {
-        SetFocusID(g.LastItemData.ID, window);
+        if (g.ActiveId != 0 && g.ActiveId != id)
+            ClearActiveID();
+        SetFocusID(id, window);
         if (!pressed && !selected)
         {
             pressed = true;