prevent div calculation before preparations

Author: levo-str

src/colvargrid_integrate.cpp

@@ -1022,6 +1022,7 @@ void colvargrid_integrate::prepare_calculations()
       }
     }
   }
+  is_calculations_prepared = true;
 }
 
 cvm::real colvargrid_integrate::get_regularized_weight(std::vector<int> &ix)

src/colvargrid_integrate.h

@@ -45,6 +45,8 @@ class colvargrid_integrate : public colvar_grid_scalar {
   void set_weighted_div();
 
   void set_div(){
+    if (!is_calculations_prepared)
+      prepare_calculations();
     if (weighted) set_weighted_div();
     else set_unweighted_div();
   };
@@ -106,6 +108,8 @@ class colvargrid_integrate : public colvar_grid_scalar {
   /// sets itself to number of available OpenMP threads
   size_t m_num_threads = 1;
 
+  bool is_calculations_prepared = false;
+
   // Get G at a specific point where G is the gradient F if there is enough observation else it's F
   // multiplied by a coefficient < 1
   void get_regularized_grad(std::vector<cvm::real> &F, std::vector<int> &ix);