Remember that a preview just got closed

[Pomax]

With an SVG source file open, and previewing turned on, the following is an infinite-preview-opening-loop:

1. open .SVG source file => preview automatically opens
2. close preview => focus goes to previous tab, which is the SVG file => preview automatically opens

Instead, the plugin should remember that the user explicitly just closed a particular preview, and not to automatically reopen the same thing that just got closed.