Fix bug where readonly fields that have error tooltip information don't display the tooltip

A field that isn't displayed in .formFieldError but that had both the
.hasErrorTooltip class and a non-empty data-error-tooltip attribute would
get a tooltip displayed because error tooltip filter property, but the
content function was looking for a .formFieldError parent.

Fields with .formFieldReadOnly and .hasErrorTooltip would show an
empty tooltip instead.