Problem description: Curreently in a CEP rule configuration form it is possible to configure an operation with "Execute when" = "Pattern matched" and "Operation" = "Discard", which in real life will never discard anything, since only newly create events can be discarded as such, but pattern match does not directly depend on event occurance in any way.
The "Discard" operation should be disabled for "Pattern matched" execute when, same as it is for "Window closed".

Steps to reproduce:

1. Open the list of CEP rules
2. Press "Create complex event processing" button
3. In the opened form press "Add" button in the "Operations table"
4. In the opened "Operations details" dialog select "Execute when" = "Pattern matched"
5. Try to select "Discard" in the "Operation" dropdown

Result: option "Discard" is enabled and can be selected, even though it is completely useless and will newer actually do anything.
Expected: same as for "Execute when" = "Window closed", operation "Discard" should be disabled in the "Operation" dropdown.