- 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.