Added a missing check for division by zero.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403578

dlib/svm/svm_c_linear_trainer.h

@@ -125,6 +125,9 @@ namespace dlib
                 cout << endl;
             }
 
+            if (current_objective_value == 0)
+                return true;
+
             if (current_error_gap/current_objective_value < eps)
                 return true;