Fix memory leak while doing drag&drop with Debug Draw in use

#1723

Source/Engine/Platform/Base/DragDropHelper.h

@@ -8,6 +8,18 @@
 #include "Engine/Scripting/ManagedCLR/MDomain.h"
 #include "Engine/Engine/Engine.h"
 #include "Engine/Platform/Platform.h"
+#if USE_EDITOR
+#if !COMPILE_WITH_DEBUG_DRAW
+#define COMPILE_WITH_DEBUG_DRAW 1
+#define COMPILE_WITH_DEBUG_DRAW_HACK
+#endif
+#include "Engine/Debug/DebugDraw.h"
+#ifdef COMPILE_WITH_DEBUG_DRAW_HACK
+#undef COMPILE_WITH_DEBUG_DRAW_HACK
+#undef COMPILE_WITH_DEBUG_DRAW
+#define COMPILE_WITH_DEBUG_DRAW 0
+#endif
+#endif
 
 /// <summary>
 /// Async DoDragDrop helper (used for rendering frames during main thread stall).
@@ -23,6 +35,10 @@ public:
         Scripting::GetScriptsDomain()->Dispatch();
         while (Platform::AtomicRead(&ExitFlag) == 0)
         {
+#if USE_EDITOR
+            // Flush any single-frame shapes to prevent memory leaking (eg. via terrain collision debug during scene drawing with PhysicsColliders or PhysicsDebug flag)
+            DebugDraw::UpdateContext(nullptr, 0.0f);
+#endif
             Engine::OnDraw();
             Platform::Sleep(20);
         }