drm_hwcomposer: during SquashAll, skip layers with kSourceNone

This complicates returning layers to the active composition on failure. They
will not go back in the correct order and this will confuse all subsequent
attempts to use the active composition.

Change-Id: Iab6fae7b4a88f97206bac08237d574ff1bfd802f
diff --git a/drmdisplaycompositor.cpp b/drmdisplaycompositor.cpp
index e6f23ff..773b696 100644
--- a/drmdisplaycompositor.cpp
+++ b/drmdisplaycompositor.cpp
@@ -1018,6 +1018,9 @@
       goto move_layers_back;
+    if (comp_plane.source_layer == DrmCompositionPlane::kSourceNone)
+      continue;
     // Out of range layers should never happen. If they do, somebody probably
     // forgot to replace the symbolic names (kSourceSquash, kSourcePreComp) with
     // real ones.