Fix serial console login
There was a change by bjorn3 to make the console login "NoPreserve". There was code in that change that disabled reading from a NoPreserve fd, which does not seem to align with the goal of making the console login NoPreserve. However, there was an obvious typo in that change.
The typo was corrected later by 4lDO2, which then caused the read from NoPreserve to fail, thus causing the serial console to stop working.
This MR allows read from the NoPreserve fd. It would be good to confirm this fix with bjorn3.