Docking: fixed calling DockContextCalcDropPosForDocking() with window in node without passing its node.

imgui.cpp

@@ -15813,6 +15813,9 @@ void ImGui::DockContextProcessUndockNode(ImGuiContext* ctx, ImGuiDockNode* node)
 // This is mostly used for automation.
 bool ImGui::DockContextCalcDropPosForDocking(ImGuiWindow* target, ImGuiDockNode* target_node, ImGuiWindow* payload_window, ImGuiDockNode* payload_node, ImGuiDir split_dir, bool split_outer, ImVec2* out_pos)
 {
+    if (target != NULL && target_node == NULL)
+        target_node = target->DockNode;
+
     // In DockNodePreviewDockSetup() for a root central node instead of showing both "inner" and "outer" drop rects
     // (which would be functionally identical) we only show the outer one. Reflect this here.
     if (target_node && target_node->ParentNode == NULL && target_node->IsCentralNode() && split_dir != ImGuiDir_None)