The game will spontaneously crash if I leave it on the menu for too long.

Put the summary of the bug you're having here
This was the first time it actually gave a crash report, other times I need to restart my computer.

What I expected to happen was...:
The game to not crash when I went away from it

What actually happened was...:
It crashed. Sorry for being so vague but there's really no way to go into great detail about this. I minimize Minecraft, go browse the internet for a couple of minutes and come back to find that the game has stopped responding.

Steps to Reproduce:
1. Start game
2. Leave it open for a bit
3. Return to find that it has crashed from a java.lang.RuntimeException: GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER