GIF decode: rectify loop count extraction

Left-shift was missing earlier.

An example affected image: https://x20web.corp.google.com/~urvang/anim3/images/anim_icc.gif

Earlier code would have set mLoopCount to 125, while correct value is 32000.

Confirmed with ImageMagick:
identify -verbose anim_icc.gif | grep 'Iterations'
  Iterations: 32000

Change-Id: I3fc9cc2febd0cc4f51c80ccf7ddcd98723881214
1 file changed