giflib -- heap overflow

Hans Jerry Illikainen reports:

A heap overflow may occur in the giffix utility included in
giflib-5.1.1 when processing records of the type
IMAGE_DESC_RECORD_TYPE' due to the allocated size of LineBuffer’
equaling the value of the logical screen width, GifFileIn->SWidth', while subsequently having GifFileIn->Image.Width’ bytes of data written
to it.