As shown in the previous commit, qemu_strtosz_MiB sometimes leaves the
result value untouched (we have to audit further to learn that in that
case, the QAPI generator says that visit_type_NumaOptions() will have
zero-initialized it), and sometimes leaves it with the value of a
partial parse before -EINVAL occurs because of trailing garbage.
Rather than blindly treating any string the user may throw at us as
valid, we should check for parse failures.

Fixes: cc001888 ("numa: fixup parsed NumaNodeOptions earlier", v2.11.0)
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20230522190441.64278-14-eblake@redhat.com>