fix: remaining issues recorded during test coverage work

- RenderManager: GPU-side members (context_, decoder_cache_,
  shader_cache_, auto_cacher_, worker_pool_, decoder_clear_timer_) were
  left uninitialized when the configured graphics backend is unknown
  (e.g. dummy); ViewerWidget then dereferenced garbage and crashed.
  Initialize them at declaration
- CurveView::SelectKeyframesOfInput ignored its reference parameter and
  selected keyframes of every connected track; select only the
  requested track's keyframes
- SeekableWidget::SeekToScenePoint dereferenced GetViewerNode()
  unconditionally; skip the playhead update when no viewer is connected
- LoadOTIOTask: unknown root schema leaked the freshly allocated
  project_ (delete + reset; OTIO is not enabled in local builds so this
  file is compile-verified by inspection only)

Locked by new tests: RenderManagerDummyBackend,
TimeRuler.SeekToScenePointWithoutViewerIsNoOp,
CurveViewTest.SelectKeyframesOfInputSelectsOnlyRequestedTrack

tests/gtest/widget_curve_keyframe_test.cpp

@@ -344,6 +344,34 @@ TEST_F(CurveViewTest, SetKeyframeTrackColorAppliesToBrush)
 	EXPECT_EQ(connection->GetBrush().color(), QColor(Qt::blue));
 }
 
+TEST_F(CurveViewTest, SelectKeyframesOfInputSelectsOnlyRequestedTrack)
+{
+	class SelectionProbeCurveView : public CurveView {
+	public:
+		using KeyframeView::IsKeyframeSelected;
+	};
+
+	SelectionProbeCurveView view;
+	view.ConnectInput(ColorTrackRef(0));
+	view.ConnectInput(ColorTrackRef(1));
+
+	NodeKeyframe *key0 =
+		InsertKeyframe(solid_, SolidGenerator::kColorInput, rational(0), 0.5, 0);
+	NodeKeyframe *key1 =
+		InsertKeyframe(solid_, SolidGenerator::kColorInput, rational(1), 0.6, 1);
+
+	// Previously the reference was ignored and keyframes of every connected
+	// track got selected.
+	view.SelectKeyframesOfInput(ColorTrackRef(0));
+	EXPECT_TRUE(view.IsKeyframeSelected(key0));
+	EXPECT_FALSE(view.IsKeyframeSelected(key1));
+
+	// Selecting the other track replaces the selection (DeselectAll first)
+	view.SelectKeyframesOfInput(ColorTrackRef(1));
+	EXPECT_FALSE(view.IsKeyframeSelected(key0));
+	EXPECT_TRUE(view.IsKeyframeSelected(key1));
+}
+
 TEST(CurveWidget, VerticalScaleRoundTripsThroughView)
 {
 	ColorManager::SetUpDefaultConfig();