timeline: treat non-primary clicks as non-moving

Fixes bug where drag would get stuck if the user right clicked on the
timeline.

app/widget/timelinewidget/timelinewidget.cpp

@@ -893,6 +893,12 @@ void TimelineWidget::ViewMousePressed(TimelineViewMouseEvent *event)
   if (GetConnectedNode() && active_tool_ != nullptr) {
     active_tool_->MousePress(event);
   }
+
+  if (event->GetButton() != Qt::LeftButton) {
+    // Suspend tool immediately if the cursor isn't the primary button
+    active_tool_->MouseRelease(event);
+    active_tool_ = nullptr;
+  }
 }
 
 void TimelineWidget::ViewMouseMoved(TimelineViewMouseEvent *event)

app/widget/timelinewidget/view/timelineviewbase.cpp

@@ -134,7 +134,9 @@ bool TimelineViewBase::PlayheadPress(QMouseEvent *event)
 {
   QPointF scene_pos = mapToScene(event->pos());
 
-  dragging_playhead_ = (scene_pos.x() >= playhead_scene_left_ && scene_pos.x() < playhead_scene_right_);
+  dragging_playhead_ = (event->button() == Qt::LeftButton
+                        && scene_pos.x() >= playhead_scene_left_
+                        && scene_pos.x() < playhead_scene_right_);
 
   return dragging_playhead_;
 }