DlgPrefEffects: restore list selection only if FocusIn reason is keyboard

[ronso0]

restoring the selection while using the keyboard works fine, though mouse clicks sent to unfocused lists that

• had an item selected previously and
• were scrolled afterwards without being focused

would select the wrong index.

---

Test main:

• go to Pref > Effects, choose chain or visible tab and
• make sure the scrollbars popup in one of the lists (decrease window height if list is too short)
• click topmost item in scrollable list
• click any item in adjacent list = selection in scrollable list is cleared
• scroll down scrollable list (don't click)
• select any item in that list
  = wrong item is selected

[ronso0]

ping @daschuer

[daschuer]

Ups, thank you for the reminder.
LGTM