Fix deadlock with Driver::write

Use a spin lock to recheck the queue size until it has room to push.

platform/windows/vcp.cpp

@@ -401,8 +401,6 @@ void VCP::writeTask() {
 				bytesWritten = 0;
 				if(WriteFile(handle, writeOp.bytes.data(), (DWORD)writeOp.bytes.size(), nullptr, &overlappedWrite))
 					continue;
-
-				onWrite();
 				
 				auto winerr = GetLastError();
 				if(winerr == ERROR_IO_PENDING) {