extra null pointer check. fixes segfault when probing driver while using SDL.
extra null pointer check. fixes segfault when probing driver while using SDL.

we really shouldnt probe gfxdrivers when using SDL.

deniskropp/DirectFB,djbclark/directfb-core-DirectFB,DirectFB/directfb,lancebaiyouview/DirectFB,kaostao/directfb,kaostao/directfb,deniskropp/DirectFB,lancebaiyouview/DirectFB,kevleyski/directfb,sklnet/DirectFB,mtsekm/test,Distrotech/DirectFB,lancebaiyouview/DirectFB,mtsekm/test,kevleyski/DirectFB-1,kevleyski/directfb,sklnet/DirectFB,deniskropp/DirectFB,kevleyski/DirectFB-1,kevleyski/directfb,mtsekm/test,kaostao/directfb,deniskropp/DirectFB,Distrotech/DirectFB,dfbdok/DirectFB1,DirectFB/directfb,dfbdok/DirectFB1,djbclark/directfb-core-DirectFB,jcdubois/DirectFB,jcdubois/DirectFB,djbclark/directfb-core-DirectFB,sklnet/DirectFB,djbclark/directfb-core-DirectFB,dfbdok/DirectFB1,DirectFB/directfb,kevleyski/DirectFB-1,lancebaiyouview/DirectFB,kevleyski/DirectFB-1,kevleyski/directfb,sklnet/DirectFB,jcdubois/DirectFB,Distrotech/DirectFB