[PATCH] evm: zero-initialize the evm_xattrs read buffer

[Pengpeng Hou]

Hi Roberto,

Thanks, I'll respin this.

I'll add the `Fixes:` tag, switch the formatting site to `snprintf()`,
and rework the empty-list handling so it does not depend on `kzalloc()`
for the terminator.

Thanks,
Pengpeng