ext4: Fix ext4_ext_journal_restart()

The ext4_ext_journal_restart() is a convenience function which checks to see if the requested number of credits is present, and if so it closes the current transaction and attaches the current handle to the new transaction. Unfortunately, it wasn't proprely checking the return value from ext4_journal_extend(), so it was starting a new transaction when one was not necessary, and returning an error when all that was necessary was to restart the handle with a new transaction.

---
This addresses the "orphan list check failed" which Frederic Bohe found once the journal credits patch was applied.

index dc6ca5e..b050259 100644
@@ -99,7 +99,7 @@ static int ext4_ext_journal_restart(handle_t *handle, int needed)
 	if (handle->h_buffer_credits > needed)
 		return 0;
 	err = ext4_journal_extend(handle, needed);
-	if (err)
+	if (err <= 0)
 		return err;
 	return ext4_journal_restart(handle, needed);
 }