vulkan: avoid duplicated app messages

When vkDebugReportMessageEXT is called, every component (layer,
vulkan::driver, or hal) supporting the extension knows how to handle it.
But only one of them should handle it.

Bug: 28120066
Change-Id: I4e746b80e0920c2c63f0aceceba1601536c6236d
diff --git a/vulkan/libvulkan/debug_report.cpp b/vulkan/libvulkan/debug_report.cpp
index 988655e..2478407 100644
--- a/vulkan/libvulkan/debug_report.cpp
+++ b/vulkan/libvulkan/debug_report.cpp
@@ -132,10 +132,11 @@
         GetData(instance).driver.DebugReportMessageEXT(
             instance, flags, object_type, object, location, message_code,
             layer_prefix, message);
+    } else {
+        GetData(instance).debug_report_callbacks.Message(
+            flags, object_type, object, location, message_code, layer_prefix,
+            message);
     }
-    GetData(instance).debug_report_callbacks.Message(flags, object_type, object,
-                                                     location, message_code,
-                                                     layer_prefix, message);
 }
 
 }  // namespace driver