Bug 1392705 - part 2: Ensure LayerManagerComposite::RenderToPresentationSurface checks the compositor widget before using it r=kats

MozReview-Commit-ID: 6EP9Pp4h5cP

--HG--
extra : rebase_source : 878dac0056cb96a6206d39bd000425578503ec2b

gfx/layers/composite/LayerManagerComposite.cpp

@@ -1059,7 +1059,16 @@ private:
 void
 LayerManagerComposite::RenderToPresentationSurface()
 {
+  if (!mCompositor) {
+    return;
+  }
+
   widget::CompositorWidget* const widget = mCompositor->GetWidget();
+
+  if (!widget) {
+    return;
+  }
+
   ANativeWindow* window = widget->AsAndroid()->GetPresentationANativeWindow();
 
   if (!window) {