textview: Set handles' mode to "none" if showing the bubble

textview: Set handles' mode to "none" if showing the bubble

show_or_hide_handles() tries to disable visibility when the popover is
shown, although it triggers a bit late, and lets the handles flash briefly
if both popover and handles try to show at the same time (eg. when
pressing on the selection of a previously unfocused textview, the handles
were previously hidden, so they try to show again on focus in).