fix shutdown crash on Windows

[oltolm]

When I shutdown ppsspp I get a crash:

Exception 0xc0000005 encountered at address 0x7ff8f7eb49f6: Access violation writing location 0x00000024

RtlWaitOnAddress (Unknown Source:0)
RtlEnterCriticalSection (Unknown Source:0)
RtlEnterCriticalSection (Unknown Source:0)
std::__1::__libcpp_recursive_mutex_lock(void* (*) [5]) (Unknown Source:0)
std::__1::recursive_mutex::lock() (Unknown Source:0)
std::__1::lock_guard<std::__1::recursive_mutex>::lock_guard[abi:se180100](std::__1::recursive_mutex&) (c:\msys64\clang64\include\c++\v1\__mutex\lock_guard.h:35)
MIPSState::Shutdown() (c:\src\ppsspp\Core\MIPS\MIPS.cpp:165)
MIPSState::~MIPSState() (c:\src\ppsspp\Core\MIPS\MIPS.cpp:161)
::__dtor_mipsr4k() (Unknown Source:0)
_execute_onexit_table (Unknown Source:0)
_execute_onexit_table (Unknown Source:0)
_execute_onexit_table (Unknown Source:0)
exit (Unknown Source:0)
exit (Unknown Source:0)
exit (Unknown Source:0)
__tmainCRTStartup (c:\M\B\src\mingw-w64\mingw-w64-crt\crt\crtexe.c:260)
WinMainCRTStartup (c:\M\B\src\mingw-w64\mingw-w64-crt\crt\crtexe.c:148)
BaseThreadInitThunk (Unknown Source:0)
RtlUserThreadStart (Unknown Source:0)

I fixed it. Not sure if it is correct, but it works.

[anr2me]

May be try to use debug build and see which thread hold the lock, or may be the thread that hold the lock already exited?
Oops sorry, since it's a crash while trying to lock, may be the lock (MIPSComp::jitLock) was already destroyed? may be checked whether MIPSComp is null or not? (i kinda forgot whether a destroyed object will become null or not tho)

[oltolm]

It's not possible to check if the lock was destroyed, but I noticed that my fix can be simplified. I skipped the call to Shutdown from the destructor, but it is simpler to just remove the call.

[hrydgard]

I guess this is alright.

I want to someday get around to redesigning the whole startup / shutdown process, it's kind of grown into a multiplatform mess...