layers: Abort logging if null debug_report ptr

If a layer were to only be enabled on the device chain
it would not have had a chance to allocate a debug_report
data structure. Just treat such cases as having debug_report
disabled.
diff --git a/layers/layer_logging.h b/layers/layer_logging.h
index 9370abd..bcae4d9 100644
--- a/layers/layer_logging.h
+++ b/layers/layer_logging.h
@@ -226,7 +226,7 @@
     const char*                 format,
     ...)
 {
-    if (!(debug_data->active_flags & msgFlags)) {
+    if (!debug_data || !(debug_data->active_flags & msgFlags)) {
         /* message is not wanted */
         return;
     }