hevc: Initialize mergecand_list to 0

Unbreak cf6090dc6252f2b276aa4133e3d73a89f4c6046c.

CC: libav-stable@libav.org
Sample-Id: hevc-conformance-LTRPSPS_A_Qualcomm_1
h264: reset ret to avoid propagating minor failures

Unbreak 772d150a6e82542c06b0c251e73dd299d98d1027.

CC: libav-stable@libav.org
Bug-Id: 750 / 905753
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>