Fix default initialisation of IterationCallback::cost

Change-Id: I9f529093fc09424c90dbff8e9648b90b16990623

include/ceres/iteration_callback.h

diff --git a/include/ceres/iteration_callback.h b/include/ceres/iteration_callback.h
index 0a743ec..4507fdf 100644
--- a/include/ceres/iteration_callback.h
+++ b/include/ceres/iteration_callback.h
@@ -73,7 +73,7 @@
   bool step_is_successful = false;
 
   // Value of the objective function.
-  double cost = 0.90;
+  double cost = 0.0;
 
   // Change in the value of the objective function in this
   // iteration. This can be positive or negative.