IsItemHovered(), ItemAdd(): Fixed seemingly unnecessary comparaison of root windows, makes IsItemHovered() more consistent with internal IsHovered().

Original test was added in 6e99688fa7 should not have been using RootWindow in the first place.
The difference between public-facing and internal versions would only be noticeable with overlapped child windows, which doesn't really happen anyway

imgui.cpp

@@ -1948,16 +1948,14 @@ bool ImGui::ItemAdd(const ImRect& bb, const ImGuiID* id)
     //if (g.IO.KeyAlt) window->DrawList->AddRect(bb.Min, bb.Max, IM_COL32(255,255,0,120)); // [DEBUG]
 
     // Set up for public-facing IsItemHovered(). We store the result in DC.LastItemHoveredAndUsable.
-    // This is roughly matching the behavior of internal IsHovered()
+    // This is roughly matching the behavior of internal-facing IsHovered()
     // - we allow hovering to be true when ActiveId==window->MoveID, so that clicking on non-interactive items such as a Text() item still returns true with IsItemHovered())
     // FIXME-OPT: Consider moving this code to IsItemHovered() so it's only evaluated if users needs it. 
-    if (g.HoveredRootWindow == window->RootWindow)
-    {
+    if (g.HoveredWindow == window)
         if (IsMouseHoveringRect(bb.Min, bb.Max))
             if (g.ActiveId == 0 || (id && g.ActiveId == *id) || g.ActiveIdAllowOverlap || (g.ActiveId == window->MoveId))
                 if (IsWindowContentHoverable(window))
                     window->DC.LastItemHoveredAndUsable = true;
-    }
 
     return true;
 }
@@ -1982,9 +1980,10 @@ bool ImGui::IsHovered(const ImRect& bb, ImGuiID id, bool flatten_childs)
     {
         ImGuiWindow* window = GetCurrentWindowRead();
         if (g.HoveredWindow == window || (flatten_childs && g.HoveredRootWindow == window->RootWindow))
-            if ((g.ActiveId == 0 || g.ActiveId == id || g.ActiveIdAllowOverlap) && IsMouseHoveringRect(bb.Min, bb.Max))
-                if (IsWindowContentHoverable(g.HoveredRootWindow))
-                    return true;
+            if (g.ActiveId == 0 || g.ActiveId == id || g.ActiveIdAllowOverlap)
+                if (IsMouseHoveringRect(bb.Min, bb.Max))
+                    if (IsWindowContentHoverable(g.HoveredRootWindow))
+                        return true;
     }
     return false;
 }