Cleanup event properly; handle error from MsgWaitForMultipleObjects

Commit 11a2809e follow-up

Change-Id: Id70a95f46655ade3b867e0377ddd5bee13993187
Reviewed-on: https://gerrit.libreoffice.org/67402
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

dtrans/source/win32/clipb/MtaOleClipb.cxx

@@ -108,6 +108,9 @@ namespace /* private */
 
                         break;
                     }
+
+                    default: // WAIT_FAILED?
+                        return false;
                 }
             }
         }
@@ -268,6 +271,10 @@ CMtaOleClipboard::~CMtaOleClipboard( )
     m_bRunClipboardNotifierThread = false;
     SetEvent( m_hTerminateClipboardChangedNotifierEvent );
 
+    // unblock whoever could still wait for event processing
+    if (m_hEvtWndDisposed)
+        SetEvent(m_hEvtWndDisposed);
+
     sal_uInt32 dwResult = WaitForSingleObject(
         m_hClipboardChangedNotifierThread, MAX_WAIT_SHUTDOWN );
 
@@ -297,6 +304,9 @@ CMtaOleClipboard::~CMtaOleClipboard( )
     if ( nullptr != m_hEvtThrdReady )
         CloseHandle( m_hEvtThrdReady );
 
+    if (m_hEvtWndDisposed)
+        CloseHandle(m_hEvtWndDisposed);
+
     if ( m_MtaOleReqWndClassAtom )
         UnregisterClassW( g_szWndClsName, nullptr );