fix: dangling OpenGL context crash and uninitialized audio frame size

- OpenGLRenderer: hold the viewer-owned QOpenGLContext in a QPointer so
  DestroyInternal() safely skips it when the context has already been
  destroyed by Qt's shared-context lifecycle. Fixes a SIGSEGV when the
  full gtest suite ran MainWindow.ConstructsOffscreenWithPanelsAndMenus
  after earlier viewer tests.
- PreviewAudioDevice: add SetParams() deriving bytes_per_frame from the
  audio format (bytes per sample * channel count) instead of staying 0.

app/render/opengl/openglrenderer.cpp

@@ -164,21 +164,26 @@ void OpenGLRenderer::PostInit()
 
 void OpenGLRenderer::DestroyInternal()
 {
+	// context_ is guarded: if a caller-owned context was already destroyed,
+	// this is null and there is nothing GL-side left to release.
 	if (context_) {
 		GL_PREAMBLE;
 
 		if (functions_ && framebuffer_) {
 			functions_->glDeleteFramebuffers(1, &framebuffer_);
 		}
-		framebuffer_ = 0;
 
 		// Delete context if it belongs to us
 		if (context_->parent() == this) {
-			delete context_;
+			delete context_.data();
 		}
+	}
+
+	// functions_ is derived from the context, so it is unusable once the
+	// context is gone; reset both regardless of the path taken above.
+	framebuffer_ = 0;
 	context_ = nullptr;
 	functions_ = nullptr;
-	}
 }
 
 void OpenGLRenderer::ClearDestination(Texture *texture, double r, double g,

app/render/opengl/openglrenderer.h

@@ -27,6 +27,7 @@
 #include <QOpenGLFunctions>
 #include <QOpenGLShader>
 #include <QOpenGLVertexArrayObject>
+#include <QPointer>
 #include <QThread>
 #include <QTimer>
 
@@ -74,7 +75,7 @@ public:
 
 	QOpenGLContext *context() const
 	{
-		return context_;
+		return context_.data();
 	}
 
 	virtual QOpenGLContext *OpenGLContext() const override
@@ -126,7 +127,11 @@ private:
 
 	GLuint CompileShader(GLenum type, const QString &code);
 
-	QOpenGLContext *context_;
+	// Guarded pointer: viewer contexts are owned by the widget that created
+	// them and may be destroyed before this renderer (e.g. when a QOpenGLWidget
+	// tears down its shared context). QPointer auto-nulls in that case so
+	// DestroyInternal() never dereferences a dangling context.
+	QPointer<QOpenGLContext> context_;
 
 	QOpenGLFunctions *functions_;
 

app/render/previewaudiodevice.cpp

@@ -42,6 +42,11 @@ bool PreviewAudioDevice::isSequential() const
 	return true;
 }
 
+void PreviewAudioDevice::SetParams(const core::AudioParams &params)
+{
+	set_bytes_per_frame(params.samples_to_bytes(1));
+}
+
 qint64 PreviewAudioDevice::readData(char *data, qint64 maxSize)
 {
 	QMutexLocker locker(&lock_);

app/render/previewaudiodevice.h

@@ -22,6 +22,8 @@
 #ifndef PREVIEWAUDIODEVICE_H
 #define PREVIEWAUDIODEVICE_H
 
+#include <olive/core/render/audioparams.h>
+
 #include "previewautocacher.h"
 
 namespace olive
@@ -42,6 +44,11 @@ public:
 
 	virtual qint64 writeData(const char *data, qint64 length) override;
 
+	// Derives the frame size from the audio format (bytes per sample per
+	// channel * channel count). Until params are set, bytes_per_frame()
+	// reports 0, i.e. "unknown".
+	void SetParams(const core::AudioParams &params);
+
 	int bytes_per_frame() const
 	{
 		return bytes_per_frame_;