Fix adding many custom fields with logging on

Fix adding many custom fields with logging on

This code is only triggered in the 'bulk' writeRecords codepath,
not in the createField codepath which is used for creating custom
fields via the UI.

To replicate: on a wmff build, turn loggin on, check out
https://gerrit.wikimedia.org/r/c/wikimedia/fundraising/crm/+/709873
and run drush update-custom-fields

Result prior to this patch: SQL syntax error message and new field
not added to logging table

Result with this patch: no error message, new field created on log
table.