effects/kscreen: don't stop effect when fade out animation is done

The screen needs to stay black until it gets enabled again, otherwise
slight timing differences can cause the screen to turn on full brightness
again immediately before turning off.

BUG: 460902

src/backends/drm/drm_output.cpp

@@ -241,10 +241,10 @@ void DrmOutput::setDpmsMode(DpmsMode mode)
         }
     } else {
         m_gpu->platform()->checkOutputsAreOn();
-        m_turnOffTimer.stop();
-        if (mode != dpmsMode() && setDrmDpmsMode(mode)) {
+        if (m_turnOffTimer.isActive() || (mode != dpmsMode() && setDrmDpmsMode(mode))) {
             Q_EMIT wakeUp();
         }
+        m_turnOffTimer.stop();
     }
 }
 

src/effects/kscreen/kscreen.cpp

@@ -102,7 +102,9 @@ void KscreenEffect::prePaintScreen(ScreenPrePaintData &data, std::chrono::millis
             state.m_timeLine.advance(presentTime);
             if (state.m_timeLine.done()) {
                 switchState(state);
-                m_waylandStates.remove(data.screen);
+                if (state.m_state == StateNormal) {
+                    m_waylandStates.remove(data.screen);
+                }
             }
         }
     }