Add is_empty to OsStr, rename path_extras to os_extras, don\'t go thr…

…ough the unicode validity checking on Windows

src/libstd/ffi/os_str.rs

@@ -283,6 +283,11 @@ impl OsStr {
         self.to_bytes().and_then(|b| CString::new(b).ok())
     }
 
+    #[unstable(feature = "os_extras", reason = "recently added")]
+    pub fn is_empty(&self) -> bool {
+        self.inner.inner.is_empty()
+    }
+
     /// Gets the underlying byte representation.
     ///
     /// Note: it is *crucial* that this API is private, to avoid

src/libstd/path.rs

@@ -1873,13 +1873,9 @@ impl Path {
     ///
     /// assert!(!path.is_empty());
     /// ```
-    #[unstable(feature = "path_extras", reason = "recently added", issue = "30259")]
+    #[unstable(feature = "os_extras", reason = "recently added", issue = "30259")]
     pub fn is_empty(&self) -> bool {
-        if let Some(b) = self.inner.to_bytes() {
-            b.is_empty()
-        } else {
-            true
-        }
+        self.inner.is_empty()
     }
 }