Implement `RawFile::dup()` completely

src/platform/src/rawfile.rs

@@ -1,20 +1,24 @@
 use core::ops::Deref;
+use sys::{open, dup, close};
 
 pub struct RawFile(usize);
 
 impl RawFile {
-    pub fn open<T: AsRef<[u8]>>(path: T, flags: usize) -> Result<RawFile> {
+    pub fn open<T: AsRef<[u8]>>(path: T, flags: usize) -> Result<RawFile, ()> {
         open(path, flags).map(RawFile)
     }
 
-    pub fn dup(&self, buf: &[u8]) -> Result<RawFile> {
-        dup(self.0, buf).map(RawFile)
+    pub fn dup(&self, _buf: &[u8]) -> Result<RawFile, ()> {
+        match dup(self.0 as i32) {
+            0 => Err(()),
+            n => Ok(RawFile(n as usize))
+        }
     }
 }
 
 impl Drop for RawFile {
     fn drop(&mut self) {
-        let _ = close(self.0);
+        let _ = close(self.0 as i32);
     }
 }