don't set response on errors
don't set response on errors

`pam_conv(3)` states that on `PAM_CONV_ERR` the application
should not set `*resp`, and this can in fact cause pam to
attempt to `free()` it, causing a crash.

Signed-off-by: Wolfgang Bumiller <bac7898f539fd233d9ce33be7a9eda13ee647930@proxmox.com>

MrFloya/pam-auth