Fix undefined shift on assumed 8-bit input.

Fix undefined shift on assumed 8-bit input.

decode_user_data() attempts to create an integer |build|
value with 8 bits of spacing for 3 components. However
each component is an int32_t, so shifting each component
is undefined for values outside of the 8 bit range.

This patch simply clamps input to 8-bits per component
and prints out a warning that the values were clamped.

Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>