_mcd_account_delete: don't assume that the account has parameters - failed accounts might not
_mcd_account_delete: don't assume that the account has parameters - failed accounts might not

This fixes NULL pointer dereferences in account-manager/bad-cm.py, in
which we create an account whose CM doesn't exist, and delete it.

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control