Regression: 'SETCONF ORPort' can kill tor process

Hi network team. Recently-ish Stem's integ tests began failing when ran with network tests ('run_tests.py --integ --target ONLINE'). Here's the repro...

My torrc...

DataDirectory /home/atagar/.tor
ORPort 9052
ControlPort 9051
ExitRelay 0

Start tor.
Connect to the control port and toggle the ORPort off and on...

% telnet localhost 9051

AUTHENTICATE
250 OK

RESETCONF ORPort
250 OK

SETCONF ORPort=9090
Connection closed by foreign host.

The tor dies with...

Jul 31 14:49:21.000 [notice] Opening OR listener on 0.0.0.0:9090
Jul 31 14:49:21.000 [warn] Can't get my x509 link cert.
Jul 31 14:49:21.000 [err] Unable to update Ed25519 keys!  Exiting.
Jul 31 14:49:21.000 [notice] Your Tor server's identity key fingerprint is 'Unnamed 4853AB6F9215A837EA3562CF4AF00713737FDF01'
Jul 31 14:49:21.000 [notice] Now checking whether ORPort 71.231.87.208:9090 is reachable... (this may take up to 20 minutes -- look for log messages indicating success)
Jul 31 14:49:21.000 [notice] Configured to measure directory request statistics, but no GeoIP database found. Please specify a GeoIP database using the GeoIPFile option.

This was with the latest tor git commit (7e4ac02).

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