Removing lastupdated column via filter in the MS Sites List Table can cause a notice

[jeremyfelt]

In WP_MS_Sites_List_Table->display_rows(), the registered column assumes that the $date set by the lastupdated column is available to it. If the lastupdated column is filtered out, $date is not available and a notice is shown.

Setting this date format is not expensive at all. the attached patch moves it to the top of display_rows() so that it is available throughout.

[SergeyBiryukov]

In 28898:

Set date format before going into the loop to avoid a PHP notice if 'lastupdated' column is filtered out.

props jeremyfelt.
fixes #27614.