guard against undefined req.agent (#313)

* Update remote_request_data.js

* suggested change

* Add unit test for request agent validation

Author: joebowbeer

packages/core/lib/segments/attributes/remote_request_data.js

@@ -14,7 +14,7 @@ function RemoteRequestData(req, res, downstreamXRayEnabled) {
 
 RemoteRequestData.prototype.init = function init(req, res, downstreamXRayEnabled) {
   this.request = {
-    url: (req.agent.protocol + '//' + req.getHeader('host') +  stripQueryStringFromPath(req.path)) || '',
+    url: (req.agent && req.agent.protocol) ? (req.agent.protocol + '//' + req.getHeader('host') +  stripQueryStringFromPath(req.path)) : '',
     method: req.method || '',
   };
 

packages/core/test/unit/segments/attributes/remote_request_data.test.js

@@ -41,5 +41,14 @@ describe('RemoteRequestData', function() {
         'https://host.com/path/to/resource'
       );
     });
+    it('should return empty url if request agent is missing', function() {
+      const requestWithoutAgent = {};
+      
+      assert.propertyVal(
+        new RemoteRequestData(requestWithoutAgent, response, true).request,
+        'url',
+        ''
+      );
+    });
   });
 });