Closes https://github.com/tpope/vim-fugitive/issues/686
For example, when running:
:Git add %
neovim throws the following exception:
E499: Empty file name for '%' or '#',
only works with ":p:h": terminal git add %
It is a result of the tabnew command, it creates a new blank tab where
"%" is empty.
This commit changes "tabnew" to "tabedit %" so you're still working on
the same file.
Once the command is done running the tab closes.
