[Why]
Link encoders are created based on its engine ID. The position of a link
encoder in an array could be null since it didn't be allocated.  Current
matching logic didn't consider this situation and could get null
encoder.

[How]
To add null encoder check to make the matching logic can go to next to
get a valid one.
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: NAric Cyr <Aric.Cyr@amd.com>
Acked-by: NRodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: NMartin Tsai <martin.tsai@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>