print more meaningful error message when trying to access individual data from a local array produced by a compute */local

src/variable.cpp

@@ -1578,6 +1578,8 @@ double Variable::evaluate(char *str, Tree **tree, int ivar)
           newtree->nextra = 0;
           treestack[ntreestack++] = newtree;
 
+        } else if (nbracket == 1 && compute->local_flag) {
+          print_var_error(FLERR,"Cannot access local data via indexing",ivar);
         } else print_var_error(FLERR,
                                "Mismatched compute in variable formula",ivar);