Eat a few more cycles on END cmds.

Fixes #3049, which apparently expects an END/FINISH to not immediately
trigger (it drawsyncs soon after, and completely expects that to
reschedule.)

Either way, it seems plausible an END would take a few more cycles than
most instructions, since it generates an interrupt.
Merge pull request #5988 from unknownbrackets/gpu-minor

Eat a few more cycles on END cmds