til_fb: fix bug in til_fb_fragment_slice_single()

Silly bug, these fragmenters need to be revisited in general to
have less copy pasta across the texture fragment and main
fragment.

Easily triggered with:
--seed=0x64daba35 '--module=compose,layers=julia\,checkers\\\,size\\\=:96\\\,pattern\\\=checkered\\\,fill_module\\\=:checkers\\\\\\\,size\\\\\\\=128\\\\\\\,pattern\\\\\\\=checkered\\\\\\\,fill_module\\\\\\\=moire\\\\\\\\\\\\\\\,type\\\\\\\\\\\\\\\=pinwheel\\\\\\\\\\\\\\\,scale\\\\\\\\\\\\\\\=1\\\\\\\\\\\\\\\,pinch\\\\\\\\\\\\\\\=0\\\\\\\\\\\\\\\,points\\\\\\\\\\\\\\\=5\\\\\\\\\\\\\\\,spin\\\\\\\\\\\\\\\=.1\\\\\\\,dynamics\\\\\\\=alternating\\\\\\\,dynamics_rate\\\\\\\=1.0\\\\\\\,fill\\\\\\\=textured\\\\\\\,fill_color\\\\\\\=0xffffff\\\\\\\,clear\\\\\\\=textured\\\\\\\,clear_color\\\\\\\=0x000000\\\,dynamics\\\=alternating\\\,dynamics_rate\\\=1.0\\\,fill\\\=textured\\\,fill_color\\\=0xffffff\\\,clear\\\=textured\\\,clear_color\\\=0x000000,texture=plasma' '--video=sdl,fullscreen=off,size=640x480'

0 files changed, 0 insertions, 0 deletions