GUI: Fix argument handling for nvim-qt --
GUI: Fix argument handling for nvim-qt --

Reported in #174, nvim-qt -- FILE causes the FILE argument to
be passed to Neovim twice, because the wrong variable was being
passed on to spawn the Neovim process.

equalsraf/neovim-qt,equalsraf/neovim-qt,equalsraf/neovim-qt,equalsraf/neovim-qt