hotfix: we do need CObjNum::to_dr() even if here and there we respect has_err()

distrib/core/HOWTO

+### first of all, check whether all tests pass
+cd /G/f2/pub
+mi
+ctest -j7
+
 cd /G/f2
 git checkout master
 git pull origin master
@@ -56,8 +61,8 @@ mkdir build
 cd build
 cmake ..
 m -j7
-ctest -j7
 mi
+ctest -j7
 
 ### upload man page (if changed)
 

pub/lib/obj.hpp

@@ -47,8 +47,8 @@ class CObjNum : public CObj
 public:
     CObjNum() : CObj() {}
     bool is_vec() const { return false; }
-//    virtual double to_dr() const { return 0.; }
-//    virtual double to_dr(int i) const { return 0.; }
+    virtual double to_dr() const { return 0.; }
+    virtual double to_dr(int i) const { return 0.; }
     virtual RObjVecNum to_vec(int repetitions) const = 0;
 };