Avoid SolarMutex assertion in a dbgutil build when exiting Impress

Change-Id: I903d078713007920574dcdb780e1dd301ce94bf6

drawinglayer/source/primitive2d/textlayoutdevice.cxx

@@ -79,6 +79,7 @@ namespace
     ImpTimedRefDev::~ImpTimedRefDev()
     {
         OSL_ENSURE(0L == mnUseCount, "destruction of a still used ImpTimedRefDev (!)");
+        const SolarMutexGuard aGuard;
         delete mpVirDev;
     }