Decoder: Updated error check while parsing num_ref_idx_lx_active.

Added an error check on the lower limit of u1_num_ref_idx_lx_active,
while parsing slice header. The minimum possible value is 1.

Bug: 64836894

Change-Id: I57056851fc135ed00f7a10af5c81eb560e9e12de
(cherry picked from commit 208c74d62a3e1039dc87818306e057877760fbaa)