timebased: set connected node before processing

Fixes #1775

app/widget/viewer/footageviewer.cpp

@@ -51,9 +51,10 @@ void FootageViewerWidget::DisconnectNodeEvent(ViewerOutput *n)
 {
   // Cache timestamp in case this footage is opened again later
   cached_timestamps_.insert(n, GetTime());
-  SetTime(0);
 
   super::DisconnectNodeEvent(n);
+
+  SetTime(0);
 }
 
 void FootageViewerWidget::StartFootageDragInternal(bool enable_video, bool enable_audio)

app/widget/viewer/viewer.cpp

@@ -532,6 +532,10 @@ void ViewerWidget::ForceRequeueFromCurrentTime()
 
 void ViewerWidget::UpdateTextureFromNode()
 {
+  if (!GetConnectedNode()) {
+    return;
+  }
+
   rational time = GetTime();
   bool frame_exists_at_time = FrameExistsAtTime(time);
   bool frame_might_be_still = ViewerMightBeAStill();