Use direct call to underlying reader because we know, that we don't h…

…ave peeked event

This allow further refactoring for supporting sequences because resolves lifetime issue
that otherwise would be introduced in one of following commits

src/de/mod.rs

@@ -260,7 +260,7 @@ where
 
     fn peek(&mut self) -> Result<&DeEvent<'de>, DeError> {
         if self.peek.is_none() {
-            self.peek = Some(self.next()?);
+            self.peek = Some(self.reader.next()?);
         }
         match self.peek.as_ref() {
             Some(v) => Ok(v),