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/render_misc_test.cpp

@@ -712,3 +712,22 @@ TEST_F(RenderMiscAutoCacherTest, CacheProxyTaskCancelledClearsPendingJobs)
 
 	cacher.SetProject(nullptr);
 }
+
+// With an unknown/dummy graphics backend the RenderManager never creates the
+// GPU-side objects. Those pointers must be null (previously they were left
+// uninitialized, so callers such as ViewerWidget dereferenced garbage and
+// crashed).
+TEST(RenderManagerDummyBackend, GpuMembersAreNullRatherThanUninitialized)
+{
+	const QVariant previous =
+		olive::Config::Current()[QStringLiteral("GraphicsBackend")];
+	olive::Config::Current()[QStringLiteral("GraphicsBackend")] =
+		QStringLiteral("dummy");
+
+	olive::RenderManager::CreateInstance();
+
+	EXPECT_EQ(olive::RenderManager::instance()->GetCacher(), nullptr);
+
+	olive::RenderManager::DestroyInstance();
+	olive::Config::Current()[QStringLiteral("GraphicsBackend")] = previous;
+}

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();

tests/gtest/widget_timeruler_playback_test.cpp

@@ -100,6 +100,20 @@ TEST(TimeRuler, SeekToScenePointWithoutTimebaseIsNoOp)
 	SUCCEED();
 }
 
+TEST(TimeRuler, SeekToScenePointWithoutViewerIsNoOp)
+{
+	EnsureAppSingletons();
+
+	// Timebase set but no viewer connected: previously dereferenced a null
+	// GetViewerNode() and crashed.
+	TimeRuler ruler;
+	ruler.SetTimebase(rational(1, 30));
+	ruler.SetScale(100.0);
+
+	ruler.SeekToScenePoint(150.0);
+	SUCCEED();
+}
+
 class PlaybackControlsTest : public ::testing::Test {
 protected:
 	void SetUp() override