CVE-2021-30015

There is a Null Pointer Dereference in function filter_core/filter_pck.c:gf_filter_pck_new_alloc_internal in GPAC 1.0.1. The pid comes from function av1dmx_parse_flush_sample, the ctx.opid maybe NULL. The result is a crash in gf_filter_pck_new_alloc_internal.