Fixed bitmap unload from graphics memory for I8 bitmaps.
Fixed bitmap unload from graphics memory for I8 bitmaps.

svn path=/trunk/libavg/; revision=2786

hoodie/libavg,yyd01245/libavg,th3infinity/libavg,th3infinity/libavg,libavg/libavg,hoodie/libavg,hoodie/libavg,libavg/libavg,th3infinity/libavg,libavg/libavg,yyd01245/libavg,scotty007/libavg,scotty007/libavg,th3infinity/libavg,libavg/libavg,scotty007/libavg,scotty007/libavg,yyd01245/libavg,hoodie/libavg,yyd01245/libavg