Steps to reproduce:
1. Using SDL as directfb's backend;
2. run any gtk app;
3. it caught signal 11, when gtk_init();


Stack trace:
None

Other information:
I checked the code, and it crashed due to：
_gdk_visual_init () in gdkvisual-directfb.c
  for (i = 0, c = 0; i < G_N_ELEMENTS (formats); i++)
    {
      IDirectFBSurface    *src;
      DFBAccelerationMask  acc;

      desc.flags = DSDESC_WIDTH | DSDESC_HEIGHT | DSDESC_PIXELFORMAT;
      desc.width       = 8;
      desc.height      = 8;
      desc.pixelformat = formats[i];
      //call direct so fail silently  is ok
      if (_gdk_display->directfb->CreateSurface (_gdk_display->directfb,
	 &desc, &src) != DFB_OK) 
        continue;

      visuals[i] = gdk_directfb_visual_create (formats[i]);

      dest->GetAccelerationMask (dest, src, &acc);

      if (acc & DFXL_BLIT || formats[i] == dlc.pixelformat)
        {

           system_visual = GDK_VISUAL (visuals[c]); <--Here is the bug, it should be 'i' not 'c' for array offset 
          c++; 			
        }

      src->Release (src);
    }