STT: do not choke on empty files

Fixes watson-developer-cloud#198

Author: nfriedly

services/speech_to_text/v1.js

@@ -471,8 +471,8 @@ function RecognizeStream(options){
         }
       } else if (data.results) {
         self.emit('results', data);
-        // note: currently there is always exactly 1 entry in the results array. However, this may change in the future.
-        if(data.results[0].final && data.results[0].alternatives) {
+        // note: currently there is always either no entries or exactly 1 entry in the results array. However, this may change in the future.
+        if(data.results[0] && data.results[0].final && data.results[0].alternatives) {
           self.push(data.results[0].alternatives[0].transcript, 'utf8'); // this is the "data" event that can be easily piped to other streams
         }
       } else {

test/resources/blank.wav

@@ -315,9 +315,21 @@ describe('integration-all-services', function() {
           assert.equal(transcription.trim(), 'thunderstorms could produce large hail isolated tornadoes and heavy rain');
           done();
         }));
-      });
     });
 
+    it('createRecognizeStream() - no words',  function (done) {
+      var recognizeStream = speech_to_text.createRecognizeStream({content_type: 'audio/l16; rate=44100'});
+      recognizeStream.setEncoding('utf8');
+      fs.createReadStream(__dirname + '/resources/blank.wav')
+        .pipe(recognizeStream)
+        .on('error', done)
+        .on('data', function(text) {
+          assert(!text, 'no text expected for an audio file with no words')
+        })
+        .on('end', done);
+    });
+  });
+
   describe('functional_dialog', function() {
     this.timeout(THIRTY_SECONDS);
     var dialog = watson.dialog(auth.dialog);