After removing last script item parameter it gives 'invalid timeout' error

Steps to reproduce:

1. Create script item with parameter (simple 'return 1' would be enough)
2. Reload configuration cache
3. Observe that item is processed normally
4. Remove all parameters of created script item
5. Reload configuration cache
6. Observe that item give 'Invalid timeout:' error

This happens because when removing all parameters the ZBX_DC_SCRIPTITEM structure where the parameters were stored is removed from cache. However this structure also stores script item timeout, so it shouldn't be removed.