Fix writeColrBox to write 0x80 instead of 128

Use 0x80 and explicitly cast down to int8_t.

Bug: http://b/29831838
Change-Id: Ibf989863ab2affdc7218f94ca073f37f5192d488
(cherry picked from commit fffb0c8fbe16ac948619b85e1eea9e65a9daa0c9)
1 file changed