don't call done twice for thrown errors inside parameterized routes

fixes #1995

lib/router/index.js

@@ -280,7 +280,7 @@ proto.process_params = function(route, req, res, done) {
         return param();
       }
     } catch (err) {
-      done(err);
+      return done(err);
     }
 
     done();

test/Router.js

@@ -111,6 +111,25 @@ describe('Router', function(){
 
       router.handle({ url: '/foo', method: 'GET' }, {}, done);
     });
+
+    it('should handle throwing inside routes with params', function(done) {
+      var router = new Router();
+
+      router.get('/foo/:id', function(req, res, next){
+        throw new Error('foo');
+      });
+
+      router.use(function(req, res, next){
+        assert(false);
+      });
+
+      router.use(function(err, req, res, next){
+        assert.equal(err.message, 'foo');
+        done();
+      });
+
+      router.handle({ url: '/foo/2', method: 'GET' }, {}, done);
+    });
   })
 
   describe('.all', function() {