1. We don't correctly check that a render target of 0u exists, only that there is at least one color attachment in entity_pass. this can cause a crash.
2. https://github.com/flutter/engine/blob/main/shell/platform/linux/fl_renderer_gl.cc#L65
3. Desktop OpenGL throws an invalid parameter error when uploading the A8 texture for the glyph atlas.
4. Desktop OpenGL throws invalid parameter when looking up extensions.

Fixing these removes most crashes but the rendering does not show up.