speech: Check if speech schema is present

The schema is provided by the sugar shell package and
in scenarios where that package is not present trying
to reference ends up in segfaults, e.g. flatpak apps.

src/sugar3/speech.py

@@ -48,6 +48,9 @@ DEFAULT_RATE = 0
 _SAVE_TIMEOUT = 500
 
 
+SPEECH_SCHEMA = 'org.sugarlabs.speech'
+
+
 # This voice names are use dto allow the translation of the voice names.
 # If espeak add new voices, we need update this list.
 
@@ -300,7 +303,11 @@ class SpeechManager(GObject.GObject):
     def save(self):
         self._save_timeout_id = -1
 
-        settings = Gio.Settings('org.sugarlabs.speech')
+        schema_source = Gio.SettingsSchemaSource.get_default()
+        if schema_source.lookup(SPEECH_SCHEMA, True) is None:
+            return False
+
+        settings = Gio.Settings(SPEECH_SCHEMA)
         settings.set_int('pitch', self._pitch)
         settings.set_int('rate', self._rate)
         logging.debug('saving speech configuration pitch %s rate %s',
@@ -308,7 +315,11 @@ class SpeechManager(GObject.GObject):
         return False
 
     def restore(self):
-        settings = Gio.Settings('org.sugarlabs.speech')
+        schema_source = Gio.SettingsSchemaSource.get_default()
+        if schema_source.lookup(SPEECH_SCHEMA, True) is None:
+            return
+
+        settings = Gio.Settings(SPEECH_SCHEMA)
         self._pitch = settings.get_int('pitch')
         self._rate = settings.get_int('rate')
         logging.debug('loading speech configuration pitch %s rate %s',