skins2: work around a deallocation problem

VlcManager and VarManager dependents on each other (a design problem)
Anyway, it is a bad idea to use instance() on any manager when deallocating ressources
as it can start anew a manager already deallocated.
Better use global variables in p_sys and act accordingly.

modules/gui/skins2/utils/var_text.cpp

@@ -219,14 +219,21 @@ void VarText::onUpdate( Subject<VarText> &rVariable, void *arg )
 void VarText::delObservers()
 {
     // Stop observing other variables
-    VlcProc *pVlcProc = VlcProc::instance( getIntf() );
+
+    VlcProc *pVlcProc = getIntf()->p_sys->p_vlcProc;
+    VarManager *pVarManager = getIntf()->p_sys->p_varManager;
+
+    if( pVlcProc )
+    {
         pVlcProc->getTimeVar().delObserver( this );
         pVlcProc->getVolumeVar().delObserver( this );
         pVlcProc->getStreamNameVar().delObserver( this );
         pVlcProc->getStreamURIVar().delObserver( this );
         pVlcProc->getStreamBitRateVar().delObserver( this );
         pVlcProc->getStreamSampleRateVar().delObserver( this );
-    VarManager *pVarManager = VarManager::instance( getIntf() );
+    }
+
+    if( pVarManager )
         pVarManager->getHelpText().delObserver( this );
 }