libbpf: Fix memory leak in bpf_program__attach_uprobe_multi

Andrii reported memory leak detected by Coverity on error path
in bpf_program__attach_uprobe_multi. Fixing that by moving
the check earlier before the offsets allocations.

Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241115115843.694337-1-jolsa@kernel.org