CYGNUM_FILEIO_MTAB_EXTRA invalid at 0

[Tad]

Following line doesn't work if CYGNUM_FILEIO_MTAB_EXTRA is 0.  Either 
ecosconfig or the init in this line needs to change.

misc.cxx
116 cyg_mtab_entry cyg_mtab_extra[CYGNUM_FILEIO_MTAB_EXTRA] 
CYG_HAL_TABLE_EXTRA(mtab) = { { NULL } };