\hyper@anchorstart in draft mode wrong number of parameters

Originally \hyper@anchorstart uses one parameter but in draft mode it is redefined to use two parameters (\def\hyper@anchorstart#1#2{#2\Hy@xspace@end}) and here comes bug with natbib.

\documentclass{book}
\usepackage{natbib}
\usepackage[draft]{hyperref}
\begin{document}
\begin{thebibliography}{1}
\bibitem[{Awwad(2016)}]{sss}
x
\end{thebibliography}
\end{document}

Tracing shows that \hyper@anchorstart is with one parameter but expects two:

\hyper@natanchorstart #1->\Hy@raisedlink {\hyper@anchorstart {cite.#1}}
#1<-sss\@extra@b@citeb 

\Hy@raisedlink ->

\hyper@anchorstart #1#2->#2\Hy@xspace@end 
#1<-cite.sss\@extra@b@citeb 
! Argument of \hyper@anchorstart has an extra }.
<inserted text> 
\par 

Reproduce the failure with the minimal book, natbib, and draft-mode hyperref document in the issue. Trace the \hyper@natanchorstart to \Hy@raisedlink call and inspect the draft-mode definition of \hyper@anchorstart. Done means the example compiles without the extra-argument error while preserving draft-mode anchor behavior.