Fix high cpu usage from iop thread

[water111]

Previously I implemented a system so the IOP code wouldn't have to run at 100% CPU usage in a busy loop, like it does in the original game. However it was not robust to the case where the game C code calls the "is the IOP done?" function in a loop as fast as possible. This fixes that issue and the CPU usage of gk remains very low when nothing is happening.

[coveralls]

Pull Request Test Coverage Report for Build 271665732

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 64.163%

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Totals
Change from base Build 271335554:	0.003%
Covered Lines:	14096
Relevant Lines:	21969

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💛 - Coveralls