Fix compilation of scene broadcaster test (#1599)

This test fails to compile with the latest version
of protobuf, which is currently available on macOS.

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

test/integration/scene_broadcaster_system.cc

@@ -320,7 +320,8 @@ TEST_P(SceneBroadcasterTest, DeletedTopic)
 
   // The id of the deleted entity should have been published
   // Note: Only model entities are currently supported for deletion
-  EXPECT_TRUE(std::find_if(delMsg.data().cbegin(), delMsg.data().cend(),
+  EXPECT_NE(delMsg.data().cend(),
+      std::find_if(delMsg.data().cbegin(), delMsg.data().cend(),
       [&cylinderModelId](const auto &_val)
       {
         return _val == cylinderModelId;