Fixes a null pointer exception (#270)

Update the logic in fragment_transcode_video_gl.xml to use a default value of false for the data binding variable 'enableNativeMuxer' whenever it is null.

litr-demo/src/main/res/layout/fragment_transcode_video_gl.xml

@@ -87,7 +87,7 @@
                 android:text="@string/transcode"
                 android:enabled="@{sourceMedia != null && targetMedia != null && targetMedia.getIncludedTrackCount() > 0 && (transformationState.state != transformationState.STATE_RUNNING)}"
                 android:padding="@dimen/cell_padding"
-                android:onClick="@{() -> transformationPresenter.startTransformation(sourceMedia, targetMedia, trimConfig, audioVolumeConfig, transformationState, enableNativeMuxer)}"/>
+                android:onClick="@{() -> transformationPresenter.startTransformation(sourceMedia, targetMedia, trimConfig, audioVolumeConfig, transformationState, enableNativeMuxer == null ? false : enableNativeMuxer)}"/>
 
             <include layout="@layout/section_transformation_progress"
                 android:id="@+id/section_transformation_progress"
@@ -117,4 +117,4 @@
 
     </androidx.core.widget.NestedScrollView>
 
-</layout>
+</layout>