update the free memory check timer on win32 as well

svn path=/trunk/KDE/kdegraphics/okular/; revision=747259

core/document.cpp

@@ -269,6 +269,8 @@ qulonglong DocumentPrivate::getFreeMemory()
 
     GlobalMemoryStatusEx (&stat);
 
+    lastUpdate = QTime::currentTime();
+
     return ( cachedValue = stat.ullAvailPhys );
 #else
     // tell the memory is full.. will act as in LOW profile