timebased: set connected node before processing

Fixes #1775

app/widget/timebased/timebasedwidget.cpp

@@ -74,17 +74,21 @@ void TimeBasedWidget::ConnectViewerNode(ViewerOutput *node)
     return;
   }
 
-  if (viewer_node_) {
+  // Set viewer node
+  ViewerOutput* old = viewer_node_;
+  viewer_node_ = node;
+
+  if (old) {
     // Call potential derivative functions for disconnecting the viewer node
-    DisconnectNodeEvent(viewer_node_);
+    DisconnectNodeEvent(old);
 
     // Disconnect length changed signal
-    disconnect(viewer_node_, &ViewerOutput::LengthChanged, this, &TimeBasedWidget::UpdateMaximumScroll);
-    disconnect(viewer_node_, &ViewerOutput::RemovedFromGraph, this, &TimeBasedWidget::ConnectedNodeRemovedFromGraph);
+    disconnect(old, &ViewerOutput::LengthChanged, this, &TimeBasedWidget::UpdateMaximumScroll);
+    disconnect(old, &ViewerOutput::RemovedFromGraph, this, &TimeBasedWidget::ConnectedNodeRemovedFromGraph);
 
     // Disconnect rate change signals if they were connected
-    disconnect(viewer_node_, &ViewerOutput::FrameRateChanged, this, &TimeBasedWidget::AutoUpdateTimebase);
-    disconnect(viewer_node_, &ViewerOutput::SampleRateChanged, this, &TimeBasedWidget::AutoUpdateTimebase);
+    disconnect(old, &ViewerOutput::FrameRateChanged, this, &TimeBasedWidget::AutoUpdateTimebase);
+    disconnect(old, &ViewerOutput::SampleRateChanged, this, &TimeBasedWidget::AutoUpdateTimebase);
 
     // Reset timebase to null
     SetTimebase(rational());
@@ -94,9 +98,6 @@ void TimeBasedWidget::ConnectViewerNode(ViewerOutput *node)
     scrollbar_->ConnectTimelinePoints(nullptr);
   }
 
-  // Set viewer node
-  ViewerOutput* old = viewer_node_;
-  viewer_node_ = node;
   emit ConnectedNodeChanged(old, node);
 
   // Call derivatives

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();