Don't trat a revwalk's ITEROVER as an error

Author: carlosmn

walk.go

@@ -173,6 +173,10 @@ func (v *RevWalk) Iterate(fun RevWalkIterator) (err error) {
 			return nil
 		}
 		if err != nil {
+			if err.(GitError).Code == ErrIterOver {
+				err = nil
+			}
+
 			return err
 		}