fix screen switching for more than two screens

BUG: 264041
FIXED-IN: 4.9.4
(cherry picked from commit 217895fb)

kwin/activation.cpp

@@ -505,11 +505,11 @@ void Workspace::setCurrentScreen(int new_screen)
         Client* ci = focus_chain[ currentDesktop()].at(i);
         if (!ci->isShown(false) || !ci->isOnCurrentDesktop() || !ci->isOnCurrentActivity())
             continue;
-        if (!ci->screen() == new_screen)
-            continue;
+        if (ci->screen() == new_screen) {
             get_focus = ci;
             break;
         }
+    }
     if (get_focus == NULL)
         get_focus = findDesktop(true, currentDesktop());
     if (get_focus != NULL && get_focus != mostRecentlyActivatedClient())