fix(jitsi-meet-web-config.postinst) allow cert and key pre-selection (#8319)

* fix(jitsi-meet-web-config.postinst) allow cert and key pre-selection

* fix(jitsi-meet-web-config.postinst) jvb-hostname gets value from db_go instead of db_get

Co-authored-by: Jakob Pfeiffer <pgp-jkp@pfeiffer.ws>

debian/jitsi-meet-web-config.postinst

             db_set jitsi-videobridge/jvb-hostname "localhost"
             db_input critical jitsi-videobridge/jvb-hostname || true
             db_go
+            db_get jitsi-videobridge/jvb-hostname
         fi
         JVB_HOSTNAME="$RET"
 
             CERT_CHOICE="$RET"
 
             if [ "$CERT_CHOICE" = "$UPLOADED_CERT_CHOICE" ] ; then
-                db_set jitsi-meet/cert-path-key "/etc/ssl/$JVB_HOSTNAME.key"
-                db_input critical jitsi-meet/cert-path-key || true
-                db_go
                 db_get jitsi-meet/cert-path-key
+                if [ -z "$RET" ] ; then
+                    db_set jitsi-meet/cert-path-key "/etc/ssl/$JVB_HOSTNAME.key"
+                    db_input critical jitsi-meet/cert-path-key || true
+                    db_go
+                    db_get jitsi-meet/cert-path-key
+                fi
                 CERT_KEY="$RET"
-                db_set jitsi-meet/cert-path-crt "/etc/ssl/$JVB_HOSTNAME.crt"
-                db_input critical jitsi-meet/cert-path-crt || true
-                db_go
                 db_get jitsi-meet/cert-path-crt
+                if [ -z "$RET" ] ; then
+                    db_set jitsi-meet/cert-path-crt "/etc/ssl/$JVB_HOSTNAME.crt"
+                    db_input critical jitsi-meet/cert-path-crt || true
+                    db_go
+                    db_get jitsi-meet/cert-path-crt
+                fi
                 CERT_CRT="$RET"
             else
                 # create self-signed certs