[orca] Add some sanity checks to prevent crashing due to GStreamer failure

[Joanmarie Diggs <joanied src gnome org>]

commit fab3115af35cd0c821f5a05d24db8206e2673f0c
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Mon Aug 31 13:21:39 2020 +0200

    Add some sanity checks to prevent crashing due to GStreamer failure
    
    GStreamer can be initialized but still fail to create an element.
    Add checks for this condition so we don't crash upon launch.
    
    See gitlab issue #161

 src/orca/sound.py | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
---
diff --git a/src/orca/sound.py b/src/orca/sound.py
index 7c7cbc73e..724db5fac 100644
--- a/src/orca/sound.py
+++ b/src/orca/sound.py
@@ -46,6 +46,8 @@ class Player:
         self._initialized = False
         self._source = None
         self._sink = None
+        self._player = None
+        self._pipeline = None
 
         if not _gstreamerAvailable:
             msg = 'SOUND ERROR: Gstreamer is not available'
@@ -108,6 +110,11 @@ class Player:
             return
 
         self._player = Gst.ElementFactory.make('playbin', 'player')
+        if self._player is None:
+            msg = 'SOUND ERROR: Gstreamer is available, but player is None'
+            debug.println(debug.LEVEL_INFO, msg, True)
+            return
+
         bus = self._player.get_bus()
         bus.add_signal_watch()
         bus.connect("message", self._onPlayerMessage)
@@ -149,8 +156,11 @@ class Player:
             element.set_state(Gst.State.NULL)
             return
 
-        self._player.set_state(Gst.State.NULL)
-        self._pipeline.set_state(Gst.State.NULL)
+        if self._player:
+            self._player.set_state(Gst.State.NULL)
+
+        if self._pipeline:
+            self._pipeline.set_state(Gst.State.NULL)
 
     def shutdown(self):
         """Shuts down the sound utilities."""