When starting a thread, put old thread at end.

This matters so the right thread is run later when scheduling switches
back.

Core/HLE/sceKernelThread.cpp

@@ -1614,7 +1614,9 @@ int sceKernelStartThread(SceUID threadToStartID, u32 argSize, u32 argBlockPtr)
 			// TODO: Maybe this happens even for worse-priority started threads?
 			dispatchEnabled = true;
 
-			__KernelChangeReadyState(currentThread, true);
+			if (cur && cur->isRunning())
+				cur->nt.status &= ~THREADSTATUS_RUNNING;
+			__KernelChangeReadyState(cur, currentThread, true);
 			hleReSchedule("thread started");
 		}
 		else if (!dispatchEnabled)