the file browser, as Pico doesn't, and since path is always assumed to
be NULL if DISABLE_BROWSER is defined, put the check for its being NULL
in a DISABLE_BROWSER #define


git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@3769 35c25a1d-7b9e-4130-9fde-d3aeb78583b8