From Laurens Voerman, "while debugging ImageSequence I had a crash, due to the very large frametimes caused by halting the program. The problem is that when the frame time exceeds the length of the entire image sequence, a looping  sequence will try to read it's _imageDataList beyond its size.
fix attached for  src/osg/ImageSequence.cpp"


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14293 16af8721-9629-0410-8352-f15c8da7e697