Avoid dereferencing NULL-pointer

As of ea23a3fd71, keyboard events that yield no text pass a NULL pointer rather
than an empty string.  file-browser.c was not updated to handle this behaviour.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Merge branch 'master' of github.com:mortehu/bra
Use fstatat instead of stat during directory scans

The stat system call needs to check permissions for each path component, and
using it during a directory scan causes race conditions when not used in
conjunction with chdir.  fstatat solves both these problems.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Ctrl-Shift-T deletes the active tab

Ctrl-W is already "delete word".  Ctrl-Shift-T means "reopen last closed tab"
in Google Chrome, so we might want to change this keyboard shortcut later.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>