The GL_CONTEXT_LOST flag is not reset when calling glGetError. This of
course bites with: "Thus, glGetError should always be called in a loop,
until it returns GL_NO_ERROR, if all error flags are to be reset."
(see https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glGetError.xhtml)
As KWin calls checkGLError from init call it can result in a freeze of
KWin. This is a regression reported multiple times since the release of
5.10.3 which enabled GLX_NV_robustness_video_memory_purge extension.
Please note that I am not able to test this change. I do not have an
NVIDIA card and are not hiting the problem. I have no way to simulate
the code. I do not know whether the change will fix the problem, it is
based on what others do. Inspiration for this change is mostly from
mutter: https://git.gnome.org/browse/mutter/commit/?id=d4d2bf0f6c1737256b921c4f1dedd3a95138cab9
BUG: 381870
FIXED-IN: 5.10.3.1