respond to reinvite request incase error (#126)

lib/call-session.js

@@ -782,6 +782,7 @@ Duration=${payload.duration} `
       this.logger.debug({opts, sdp: response.sdp}, 'CallSession:_onReinvite: (answer) sending back upstream');
       res.send(200, {body: response.sdp});
     } catch (err) {
+      res.send(err.status || 500);
       this.logger.error(err, 'Error handling reinvite');
     }
   }