Fix a Parcel `collection == null` exception.

This is caused by the Voice features being set to null. The fix in
Android Marshmallow is to make onGetFeaturesForLanguage return an
empty HashSet object. This does not work for eSpeak because:

  1.  eSpeak was overriding onGetVoices and initializing each Voice's
      features to null;

  2.  the bug is still present on Lollipop.

Thus, the fix here is two-fold:

  1.  make onGetVoices use onGetFeaturesForLanguage;

  2.  make onGetFeaturesForLanguage return an empty HashSet, so that
      eSpeak does not crash on Lollipop either.

android/eSpeakTests/src/com/reecedunn/espeak/test/TextToSpeechServiceTest.java

 import com.reecedunn.espeak.Voice;
 
 import java.util.Locale;
+import java.util.Set;
 
 import static com.reecedunn.espeak.test.TtsMatcher.isTtsLangCode;
 import static org.hamcrest.MatcherAssert.assertThat;
             return super.onLoadLanguage(language, country, variant);
         }
 
+        public Set<String> onGetFeaturesForLanguage(String language, String country, String variant) {
+            return super.onGetFeaturesForLanguage(language, country, variant);
+        }
+
         public Voice getActiveVoice() {
             return mMatchingVoice;
         }
                 assertThat(locale.getISO3Language(), is(data.javaLanguage));
                 assertThat(locale.getISO3Country(), is(data.javaCountry));
                 assertThat(locale.getVariant(), is(data.variant));
+
+                Set<String> features = mService.onGetFeaturesForLanguage(data.javaLanguage, data.javaCountry, data.variant);
+                assertThat(features, is(notNullValue()));
+                assertThat(features.size(), is(0));
             }
         }
     }

android/eSpeakTests/src/com/reecedunn/espeak/test/TextToSpeechTest.java

             assertThat(voice.getLocale().getLanguage(), is(data.javaLanguage));
             assertThat(voice.getLocale().getCountry(), is(data.javaCountry));
             assertThat(voice.getLocale().getVariant(), is(data.variant));
-            assertThat(voice.getFeatures(), is(nullValue()));
+            assertThat(voice.getFeatures(), is(notNullValue()));
+            assertThat(voice.getFeatures().size(), is(0));
             assertThat(voice.getLatency(), is(android.speech.tts.Voice.LATENCY_VERY_LOW));
             assertThat(voice.getQuality(), is(android.speech.tts.Voice.QUALITY_NORMAL));
 
             assertThat(voice2.getLocale().getLanguage(), is(data.javaLanguage));
             assertThat(voice2.getLocale().getCountry(), is(data.javaCountry));
             assertThat(voice2.getLocale().getVariant(), is(data.variant));
-            assertThat(voice2.getFeatures(), is(nullValue()));
+            assertThat(voice2.getFeatures(), is(notNullValue()));
+            assertThat(voice2.getFeatures().size(), is(0));
             assertThat(voice2.getLatency(), is(android.speech.tts.Voice.LATENCY_VERY_LOW));
             assertThat(voice2.getQuality(), is(android.speech.tts.Voice.QUALITY_NORMAL));
         }

android/src/com/reecedunn/espeak/TtsService.java

 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
 
 /**
  * Implements the eSpeak engine as a {@link TextToSpeechService}.
         return match.second;
     }
 
+    @Override
+    protected Set<String> onGetFeaturesForLanguage(String lang, String country, String variant) {
+        return new HashSet<String>();
+    }
+
     @Override
     public String onGetDefaultVoiceNameFor(String language, String country, String variant) {
         final Voice match = getDefaultVoiceFor(language, country, variant).first;
         for (Voice voice : mAvailableVoices.values()) {
             int quality = android.speech.tts.Voice.QUALITY_NORMAL;
             int latency = android.speech.tts.Voice.LATENCY_VERY_LOW;
-            voices.add(new android.speech.tts.Voice(voice.name, new Locale(voice.locale.getISO3Language(), voice.locale.getISO3Country(), voice.locale.getVariant()), quality, latency, false, null));
+            Locale locale = new Locale(voice.locale.getISO3Language(), voice.locale.getISO3Country(), voice.locale.getVariant());
+            Set<String> features = onGetFeaturesForLanguage(locale.getLanguage(), locale.getCountry(), locale.getVariant());
+            voices.add(new android.speech.tts.Voice(voice.name, locale, quality, latency, false, features));
         }
         return voices;
     }