Don't append strings for error logging

api/_apimeta/auth.go

api/custom/exports.go

api/custom/purge.go

api/custom/quarantine.go

api/r0/download.go

api/r0/preview_url.go

api/r0/thumbnail.go

api/r0/upload_async.go

api/r0/upload_sync.go

api/unstable/info.go

api/unstable/local_copy.go

...rollers/maintenance_controller/maintainance_controller.go

controllers/preview_controller/preview_resource_handler.go

controllers/upload_controller/upload_controller.go

pipelines/_steps/upload/lock.go

storage/datastore/ds_file/file_store.go

url_previewers/calculated_previewer.go

url_previewers/oembed_previewer.go

url_previewers/opengraph_previewer.go