BUG #15688: psql cannot connect to database which uses TLS nginx reverse proxy with SSL client auth

The following bug has been logged on the website:

Bug reference: 15688
Logged by: Magnus
Email address: jahnen(at)in(dot)tum(dot)de
PostgreSQL version: 11.1
Operating system: ArchLinux
Description:

```
psql "port=9876 host=****.me user=docker
sslcert=/home/magnus/mep/ca_mqtt/db.crt
sslkey=/home/magnus/mep/ca_mqtt/db_nopasswd.key
sslrootcert=/home/magnus/mep/ca_mqtt/ca.crt sslmode=require"
psql: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
```

nginx logs:
```

2019/03/12 15:35:59 [info] 6#6: *359 SSL_do_handshake() failed (SSL:
error:1408F10B:SSL routines:ssl3_get_record:wrong version number) while SSL
handshaking, client: 84.138.94.156, server: 0.0.0.0:9876,
2019/03/12 15:40:22 [info] 6#6: *488 SSL_do_handshake() failed (SSL:
error:1408F10B:SSL routines:ssl3_get_record:wrong version number) while SSL
handshaking, client: 84.138.94.156, server: 0.0.0.0:9876,
2019/03/12 15:40:16 [info] 6#6: *485 SSL_do_handshake() failed (SSL:
error:1408F10B:SSL routines:ssl3_get_record:wrong version number) while SSL
handshaking, client: 84.138.94.156, server: 0.0.0.0:9876,
2019/03/12 15:36:41 [info] 6#6: *411 SSL_do_handshake() failed (SSL:
error:1408F10B:SSL routines:ssl3_get_record:wrong version number) while SSL
handshaking, client: 84.138.94.156, server: 0.0.0.0:9876
```

See also here:
https://youtrack.jetbrains.com/issue/DBE-7814