Special enum item when no sound is found

This happens when you build without sound libraries and such.
Without that the console is spammed with tons of RNA messages because
the enum is empty.

source/blender/makesrna/intern/rna_userdef.c

@@ -486,6 +486,13 @@ static const EnumPropertyItem *rna_userdef_audio_device_itemf(bContext *UNUSED(C
 		RNA_enum_item_add(&item, &totitem, &new_item);
 	}
 
+#ifndef NDEBUG
+	if (i == 0) {
+		EnumPropertyItem new_item = {i, "SOUND_NONE", 0, "No Sound", ""};
+		RNA_enum_item_add(&item, &totitem, &new_item);
+	}
+#endif
+
 	/* may be unused */
 	UNUSED_VARS(index, audio_device_items);