qt: destroy the current compositor when it's unable to create an interface

modules/gui/qt/maininterface/compositor.cpp

@@ -85,7 +85,11 @@ Compositor* CompositorFactory::createCompositor()
         {
             Compositor* compositor = compositorList[m_compositorIndex].instanciate(m_intf);
             if (compositor->init())
+            {
+                //avoid looping over the same compositor if the current ones fails further initialisation steps
+                m_compositorIndex++;
                 return compositor;
+            }
         }
     }
     msg_Err(m_intf, "no suitable compositor found");

modules/gui/qt/qt.cpp

@@ -772,7 +772,11 @@ static void *Thread( void *obj )
                 break;
             ret = p_intf->p_compositor->makeMainInterface(p_intf->p_mi);
             if (!ret)
+            {
                 p_intf->p_compositor->destroyMainInterface();
+                delete p_intf->p_compositor;
+                p_intf->p_compositor = nullptr;
+            }
         } while(!ret);
 
         if (!ret)