[FIX] web_editor: fix drag and drop when drop zones are too close

Before this commit, the preview of the dragged snippet didn't work
when moving a dragged snippet from a drop zone to an other drop zone
when there was no space between those drop zones.

It is because, in this case, the over event of the second drop zone is
triggered before the out event of the first drop zone.

task-2312878

closes odoo/odoo#66148

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>