nanodbc:bugfix: describe_data: if unsuccesful cleanup (#908)

upstream: nanodbc/nanodbc#427

Author: detule

src/nanodbc/nanodbc.cpp

@@ -2132,7 +2132,10 @@ class statement::statement_impl
             &param_descr_data_[param_index].scale_,
             &nullable);
         if (!success(rc))
+        {
+            param_descr_data_.erase(param_index);
             NANODBC_THROW_DATABASE_ERROR(stmt_, SQL_HANDLE_STMT);
+        }
     }
 
     void describe_parameters(