Immediately close a flyout when opening another one. Prevents brief occurrence...

Immediately close a flyout when opening another one. Prevents brief occurrence of two flyouts at once. Props SergeyBiryukov. fixes #19575 for trunk

git-svn-id: https://core.svn.wordpress.org/trunk@19647 1a063a9b-81f0-0310-95a4-ce76da25c4cd