Graphs and Graphs prototypes in some cases are able to save improper values to the database.

Steps to reproduce:

1. Navigate to the graphs and create one.
2. Add at least one item. Save the graph.
   
3. Check the graph item rows "calc_fnc" and "type" of the created graph in the database.
   
4. Open the created graph and change its type to Stacked.
   
5. Save the graph.
6. Check again the graph item rows "calc_fnc" and "type" of the created graph in the database.
   For version 7.0 you will see:
   
   And for version 7.4 and master you will see:
   
7. Once more open the graph and change its type back to Normal. Save it.
8. Check again the graph item rows "calc_fnc" and "type" of the created graph in the database.
   

Result 1: For version 7.4 and master the graph items have invalid value "1" for "type" field.
Expected: The "type" field must contains proper value (0 or 2 according to documentation)

Result 2: For all versions value for "calc_fnc" field have not changed to default after switching graph back to Normal type.
Expected: The "calc_fnc" should be changed to default.