7045354: Korean IME's Hanja candidate window is not displayed on IMFDemo

Reviewed-by: art, ant

src/windows/native/sun/windows/awt_Component.cpp

@@ -3715,7 +3715,10 @@ void AwtComponent::OpenCandidateWindow(int x, int y)
             SetCandidateWindow(iCandType, x-rc.left, y-rc.top);
     }
     if (m_bitsCandType != 0) {
-        ::DefWindowProc(GetHWnd(), WM_IME_NOTIFY, IMN_OPENCANDIDATE, m_bitsCandType);
+        HWND proxy = GetProxyFocusOwner();
+        // REMIND: is there any chance GetProxyFocusOwner() returns NULL here?
+        ::DefWindowProc((proxy != NULL) ? proxy : GetHWnd(),
+                        WM_IME_NOTIFY, IMN_OPENCANDIDATE, m_bitsCandType);
     }
 }