Improved solve method

Author: ankane

ext/or-tools/constraint.cpp

@@ -471,7 +471,7 @@ void init_constraint(Rice::Module& m) {
                     exception = e;
                     stop = true;
                   }
-                  callback.call("response=", Qnil);
+                  callback.call("response=", Object(Qnil));
                 });
 
                 if (stop) {

lib/or_tools/cp_solver.rb

@@ -8,10 +8,8 @@ class CpSolver
 
     def solve(model, observer = nil)
       @response = _solve(model, parameters, observer)
-      @response.status
-    ensure
-      # avoid GC issue
       observer.response = @response if observer
+      @response.status
     end
 
     def value(var)