Isso corresponde ao que você deseja:
\{\h*\R\K\h*\R|\R\K\h*\R(?=\h*\})
//added__^^^
Explicação:
\{ : open brace
\h* : 0 or more horizontal spaces
\R : any kind of line break
\K : forget all we have seen until this position
\h* : 0 or more horizontal spaces
\R : any kind of line break
| : OR
\R : any kind of line break
\K : forget all we have seen until this position
\h* : 0 or more horizontal spaces
\R : any kind of line break
(?= : positive lookahead
\h* : 0 or more horizontal spaces
\} : close brace
) : end lookahead