Improve readability of an error check in set_non_blocking

Author: tbu-

src/libstd/sys/windows/mod.rs

@@ -194,11 +194,11 @@ pub fn wouldblock() -> bool {
 
 pub fn set_nonblocking(fd: sock_t, nb: bool) {
     let mut set = nb as libc::c_ulong;
-    (if unsafe { c::ioctlsocket(fd, c::FIONBIO, &mut set) } != 0 {
-        Err(last_error())
-    } else {
-        Ok(())
-    }).unwrap();
+    if unsafe { c::ioctlsocket(fd, c::FIONBIO, &mut set) } != 0 {
+        // The above function should not return an error unless we passed it
+        // invalid parameters. Panic on errors.
+        Err(last_error()).unwrap();
+    }
 }
 
 pub fn init_net() {