cid#1645104 Data race condition

and

cid#1645088 Data race condition
cid#1645086 Data race condition

presumably the mutex is just for maBuffered2DDecomposition, otherwise
setting maLastAccess with the mutex held implies all the other maLastAccess
uses should be protected with that mutex

Change-Id: I918b8854a2abbb8436200c98cf545e217b19bba6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/183244
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolan.mcnamara@collabora.com>

drawinglayer/source/primitive2d/BufferedDecompositionPrimitive2D.cxx

@@ -82,9 +82,9 @@ void BufferedDecompositionPrimitive2D::get2DDecomposition(
         // manipulated (e.g. deleted)
         Primitive2DReference xTmp;
         {
+            maLastAccess = std::chrono::steady_clock::now();
             // only hold the lock for long enough to get a valid reference
             std::lock_guard Guard(maCallbackLock);
-            maLastAccess = std::chrono::steady_clock::now();
             if (!maBuffered2DDecomposition)
             {
                 maBuffered2DDecomposition = create2DDecomposition(rViewInformation);