tdf#112646 Flush the clipboard holding SolarMutex

It seems Desktop::terminate can be called with or without the
SolarMutex. So make sure we actually hold the mutex to release it
correctly when flushing the clipboard on termination.

Change-Id: Ie42daf5dba0f4208318a8c1fe463cd3a80dd9141
Reviewed-on: https://gerrit.libreoffice.org/42802Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

framework/source/services/desktop.cxx

@@ -322,11 +322,12 @@ sal_Bool SAL_CALL Desktop::terminate()
 
         // The clipboard listener needs to be the first. It can create copies of the
         // existing document which needs basically all the available infrastructure.
-        impl_sendTerminateToClipboard();
-
-        impl_sendNotifyTerminationEvent();
         {
-            SolarMutexGuard aGuard;
+            SolarMutexResettableGuard aGuard;
+            impl_sendTerminateToClipboard();
+            aGuard.clear();
+            impl_sendNotifyTerminationEvent();
+            aGuard.reset();
             Scheduler::ProcessEventsToIdle();
         }