fixed a few crashes resulting from the fs library

modules/lib/fs.lua

@@ -42,6 +42,7 @@ do
  function fs.open(p,m)
   local _,d,p = fs.resolve(p)
   local d = fT[d]
+  if d then
    local f,C=d.open(p,m),hT._c
    if f then
     hT._c = C + 1
@@ -50,6 +51,7 @@ do
    end
    return false
   end
+ end
  function fs.close(h)
   if hT[h] then
    hT[h][1].close(hT[h][2])
@@ -99,8 +101,10 @@ do
  end
  function fs.exists(s)
   local _,d,p = fs.resolve(s)
+  if d then
    return fT[d].exists(p)
   end
+ end
  function fs.isdir(s)
   local _,d,p = fs.resolve(s)
   return fT[d].isDirectory(p)