plugin-ls: Stop closing the file browser when opening a file from it

Currently with a file browser, opening one of the files closes the file browser.

But this behavior is inconvenient as it breaks all the point of having a file browser instead of a file chooser. Indeed, the file browser might be used as a bigger view of a folder, which can be tiled like other panes (e.g. editor, terminal), to have a convenient workflow inside this folder.