Merge branch 'libbpf: fix fuzzer-reported issues'

Shung-Hsi Yu says:

====================

Hi, this patch set fixes several fuzzer-reported issues of libbpf when
dealing with (malformed) BPF object file:

- patch #1 fix out-of-bound heap write reported by oss-fuzz (currently
  incorrectly marked as fixed)

- patch #2 and #3 fix null-pointer dereference found by locally-run
  fuzzer.

v2:
- Rebase to bpf-next
- Move elf_getshdrnum() closer to where it's result is used in patch #1, as
  suggested by Andrii
  - Touch up the comment in bpf_object__elf_collect(), replacing mention of
    e_shnum with elf_getshdrnum()
- Minor wording change in commit message of patch #1 to for better readability
- Remove extra note that comes after commit message in patch #1

v1: https://lore.kernel.org/bpf/20221007174816.17536-1-shung-hsi.yu@suse.com/


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Signed-off-by: Andrii Nakryiko <andrii@kernel.org>