fix(PIThread): remove spurious unlock() in _waitForFinish

The function called unlock() on thread_mutex without a matching
lock(), causing UB on Windows (releasing an unowned critical
section) or silently dropping a user-held lock.

libs/main/thread/pithread.cpp

@@ -1080,7 +1080,6 @@ bool PIThread::_waitForFinish(PISystemTime max_tm) {
 	if (!running_) return true;
 #ifdef WINDOWS
 	if (!isExists(PRIVATE->thread)) {
-		unlock();
 		return true;
 	}
 #endif